back to indexBiological Influences On Sex, Sex Differences & Preferences | Huberman Lab Podcast #14
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Welcome to the Huberman Lab Podcast,
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where we discuss science and science-based tools
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for everyday life.
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I'm Andrew Huberman,
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and I'm a professor of neurobiology and ophthalmology
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at Stanford School of Medicine.
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This podcast is separate from my teaching
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and research roles at Stanford.
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It is, however, part of my desire and effort
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to bring zero cost to consumer information
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about science and science-related tools.
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In keeping with that theme,
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I'd like to thank the sponsors of today's podcast.
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Our first sponsor is InsideTracker.
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InsideTracker is a personalized nutrition platform
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that analyzes data from your blood and DNA
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to help you better understand your body
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and help you reach your health goals.
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I'm a big believer in blood tests and DNA tests
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for the simple reason that many of the factors
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that are important for your short-term and long-term health
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and overall wellbeing can only be analyzed
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from blood and DNA tests,
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things like metabolic factors and hormone levels
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really can only be assessed accurately from blood and DNA.
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The thing I like about InsideTracker
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is you don't just get back levels of different hormones
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and metabolic factors and so forth,
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you also get directives.
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It has a dashboard that's very easy to use
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that tells you based on your data
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what sorts of foods you might want to eat more of
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what forms of exercise you might want to do more of
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It's really a wonderful way to assess
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how your behaviors and lifestyle choices
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are interacting with what's going on
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deep within your biology.
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InsideTracker makes all of that super easy to understand.
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It's also really easy to get the blood tests
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and DNA tests taken.
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You can go to a local location
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or they can send somebody to your home if you prefer that.
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If you'd like to try InsideTracker,
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you can visit insidetracker.com slash Huberman
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to get 25% off any of InsideTracker's plans.
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Use the code Huberman at checkout.
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That's insidetracker.com slash Huberman
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to get 25% off any of InsideTracker's plans
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and use the code Huberman at checkout.
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Today's episode is also brought to you by Helix Sleep.
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Helix Sleep makes mattresses and pillows
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that are designed to meet your sleep needs
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in order to optimize your sleep.
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I've done several episodes of this podcast
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and there's a ton of information out there
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pointing to the fact that getting really deep
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restful sleep each night is vital
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for mental and physical health.
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And the mattress that you sleep on and the pillow
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that you use is very important for getting optimal sleep.
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Helix Sleep has a brief two minute quiz that you can take.
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It asks you questions like, do you sleep on your side
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or your back or your stomach, or maybe you don't know,
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do you tend to run hot or cold as you sleep
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or maybe you don't know.
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That two minute quiz matches you to a mattress and pillow
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that's ideal for your sleep needs.
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I took this quiz, I matched to the mattress
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they call the Dusk D-U-S-K
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and I've been sleeping on the Dusk mattress for many months
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now and I've been sleeping better than I ever have before.
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It's really wonderful to have a really good night's sleep
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on a consistent basis, it's a total game changer.
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So if you're interested in upgrading your mattress,
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you can go to helixsleep.com slash Huberman,
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take their two minute sleep quiz
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and they'll match you to a customized mattress
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and you'll get up to $200 off any of their mattress orders
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and two free pillows.
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So that's helixsleep.com slash Huberman,
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take the two minute sleep quiz,
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they'll match you to a mattress
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and if you order one of their mattresses,
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you'll get up to $200 off any of their mattresses
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and two free pillows.
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They have a 10 year warranty
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and you get to try out the mattress
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for a hundred nights risk-free
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and if you don't like it, they'll pick it up
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If you love it, then you keep it
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and I think there's a very good chance
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that you're going to love it, I certainly love mine.
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And today's episode is also brought to you
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by Athletic Greens.
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Athletic Greens is an all-in-one
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vitamin mineral probiotic drink.
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I started using Athletic Greens way back in 2012
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and so I'm delighted that they're sponsoring the podcast.
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I started using Athletic Greens
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because I found it rather confusing
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to figure out what vitamins and minerals to take.
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And Athletic Greens, I get all the vitamins and minerals
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I need to cover my bases.
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As well, probiotics are really important.
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Probiotics have been shown now in numerous studies
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to be important for the gut microbiome,
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which impacts the gut brain axis
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as well as various aspects of bodily health.
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So in Athletic Greens, I get vitamins,
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minerals and probiotics.
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I also really liked the way it tastes.
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It's a greens drink, so you mix it with some water.
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You could mix it with something else like juice if you like.
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I mix mine with water and lemon juice
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and I drink it once or twice a day.
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If you want to try Athletic Greens,
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you can go to athleticgreens.com slash Huberman.
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And if you do that, you'll claim their special offer,
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which is to get a year supply of vitamin D3K2.
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There's now also a wealth of data
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showing that vitamin D3 is important
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for various aspects of brain and body health.
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So that's athleticgreens.com slash Huberman
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for Athletic Greens and the year supply of vitamin D3K2.
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You'll also get five free travel packets.
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The travel packets are just a really convenient way
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to take Athletic Greens when you're on the road,
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in the car or on a plane, or just moving around.
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You just empty one of the packets into a water bottle
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or a glass and mix it up really quickly.
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It saves any kind of mess or anything of that sort.
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So once again, athleticgreens.com slash Huberman
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to get vitamin D3K2, that's a year supply
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and the five free travel packs.
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It's a new month, which means it's a new topic
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here at the Huberman Lab Podcast.
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For the next four or so episodes,
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we're going to be talking all about hormone effects
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on the brain and body.
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So that's a huge number of different topics.
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We're going to talk about sex.
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We're going to talk about reproduction.
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We're going to talk about puberty a little bit more.
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We talked about that in the previous episode.
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We're going to talk about menopause.
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We're going to talk about birth control.
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We are going to talk about aggression, competition,
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Basically, we're going to cover as much about hormones
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as we possibly can in this month.
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And in doing so, we are going to go deep
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into tools and protocols.
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We are also going to talk about a lot of tools
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that relate to things that you might not want to do
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in order to optimize hormone health,
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regardless of stage of life or your goals, et cetera.
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So it's sure to be a month rich with discussion,
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rich with tools, and you're going to learn
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a lot of neuroscience and endocrinology.
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There's actually a field of neuroendocrinology.
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It's actually where I started my graduate work.
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I did a master's in it,
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which is only to say that I love the topic.
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I have a lot of friends that work on this topic,
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many of whom I've consulted for these episodes,
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and I'm really excited to share the information with you.
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Before we dive into today's episode,
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all about emotions and sex,
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I want to just have a few announcements
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that are designed to point you to some useful resources.
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Last episode, talking about the science of emotions
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and relationships, I mentioned the Mood Meter app.
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The Mood Meter app was developed by people out
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at Yale University who study the biology
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and psychology of emotions.
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It's a really wonderful app.
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However, many of you quickly told me
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that the Mood Meter app isn't available in your area.
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You went to the link we posted
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and it just was saying not available in your area.
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The situation was actually a lot worse than that.
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The situation was that when we recorded the episode,
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the Mood Meter app was working.
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I know because I downloaded a fresh copy of it to my phone.
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And then in the ensuing weekend,
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they took the Mood Meter app down for some repairs.
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The Mood Meter app is now up.
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I want to be really clear.
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It's not an app I'm affiliated with.
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I'm just mentioning it to you.
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They don't know me.
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I know them, but they don't know me.
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So we don't have any kind of business relationship.
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They do charge 99 cents for the app.
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I think the free version has disappeared
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in the last year or so.
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So that's Mood Meter app.
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We'll provide the link again
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and the link should be working.
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Hopefully they won't take it down again
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in between this announcement
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and the release of this episode.
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Also just want to take a step back for a moment
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and talk a little bit about the logic
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of how to make the most of the information
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on the Huberman Lab Podcast.
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I tend to throw out a lot of information
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about a given topic.
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Many of you have pointed out, however,
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that I don't cover certain things.
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And once again, I'll just say,
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the goal is always to be accurate,
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but there's no way I can be exhaustive.
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There's no way I can cover everything
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for a particular topic.
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The good news is we have time.
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My goal, at least in the first year
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of the Huberman Lab Podcast,
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is to give you a basis,
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a foundation in these different topics
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of neuroplasticity, focus, sleep, hormones, et cetera.
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And of course, to provide tools along the way.
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We are going to host guests.
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I've actually started recording
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with some of these guests already.
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And even those episodes will include a little,
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what we call primer,
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a little description of the basics of a given topic
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so that you can get more information from those topics.
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My goal really is to educate you in these topics,
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give you a foundation in these topics
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and allow you to start exploring them here in the episodes
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with our future guests,
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but also in other podcasts and books
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and other sources of information.
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So for those of you that are saying
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it's too much information,
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I just encourage you to remind yourself
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that you have a pause button,
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you can return to it, everything's timestamp.
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For those of you who feel it's not enough information,
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I'm not covering enough,
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just know that this is just the beginning.
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We intend to do this for a very long time
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and we will be thorough over time.
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So thanks for your patience.
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And please be patient with yourselves.
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There's no reason why you have to digest
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all the information in one swoop.
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The other thing is that I've been told
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both that I speak too fast and speak too slow.
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So there's a wonderful solution to this.
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If I speak too fast or too slow,
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you can adjust the speed in YouTube.
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If you're listening in a different format,
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I think you also can adjust the speed of playback.
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So that's something that wouldn't be possible
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in the classroom, but you may find useful.
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And then last but not least,
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I want to point people again to this NSDR,
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non-sleep deep rest protocol
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that the folks over at Made For
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have put out as a free resource.
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It does, as many of you pointed out,
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bear resemblance to things like yoga nidra,
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other forms of meditation.
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But what we've done is we've stripped out intentions
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or any kind of the verbiage related
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to what some people might perceive
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as kind of related to the yoga community
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or specific to kind of new agey type techniques,
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not because we don't like yoga nidra.
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In fact, I've done yoga nidra daily
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for almost the last, goodness, eight years of my life.
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I love yoga nidra,
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but sometimes the complicated language can be a separator
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and can discourage people from taking on these protocols
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that are extremely useful.
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So NSDR is intentionally generic.
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It's designed to bring you into a state of deep relaxation
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through a combination of breathing and body scan.
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There's the YouTube script over at Made For,
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which is linked in the caption.
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And many people find that they prefer that
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to scripts like yoga nidra scripts
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where they're doing intentions
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and they're hearing a lot of kind of unusual language
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around the process.
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This is just very basic and I hope you'll enjoy it.
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And if you prefer the more typical yoga nidra scripts,
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then go with those.
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There are many of them available
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on the internet and elsewhere.
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And last but not least,
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I want to point out that all our episodes now
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are subtitled both in English and in Spanish.
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So for those of you that prefer
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to digest this information in Spanish,
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that's now available to you in the subtitles.
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Today, we're going to talk about the science of sex,
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in particular sexual differentiation.
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Now that's a complicated topic
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because sex is both a adjective, a noun, and a verb,
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depending on the context.
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Today, we're going to talk about the hormonal effects
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and the neural effects of particular events
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that happen during development
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and how those guide adolescent and adult behavior,
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including sexual preference.
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It's an area that's fascinating
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and for which there are actually
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very solid textbook findings.
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So textbook findings means that there are many studies
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that have been aggregated over decades
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that point to what we now know to be absolute truths
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in terms of how hormones affect brain development,
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how the brain impacts hormonal development,
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and how those interact to control behavior, for instance.
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We are also going to talk about reproduction, the verb sex.
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And of course, sex, the verb,
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can also be carried out independent of reproduction.
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It's not always in particular in humans
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just to produce offspring.
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So that's going to be covered in the next episode,
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but you absolutely need to understand the information
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in this episode in order to make sense of the information
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in the next episode.
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So today we're going to explore hormones,
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what they are, how they work,
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what leads to masculinization or feminization
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of the brain and body.
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I'll just throw out one really interesting fact
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that perhaps most of you didn't realize
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that hormones have direct effects on the body.
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Most people know that because there are hormone differences
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and sex differences in bodies
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in terms of genitalia and body hair,
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distribution of body hair, et cetera.
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But there are also effects of hormones on the brain directly
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and believe it or not,
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there are also effects on the spinal cord,
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on the neurons and structures within the spinal cord
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that impact in a very direct way
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what sorts of behaviors are possible.
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So it's a fascinating area.
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You might notice I'm going to go a little bit more slowly
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through this topic than I normally do.
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I want to be extremely careful with my language.
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Some of these topics,
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some of you may be thinking are extremely sensitive, right?
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any discussion about sex and reproduction
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is a sensitive one,
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but today we're just talking about the biology.
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We're not getting into the cultural constraints
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or the cultural dialogue.
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What we're trying to do today is really get to the biology,
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the physiology, the endocrinology and the behavior.
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So let's start by talking about what hormones are
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just to remind you and what they do.
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Hormones by definition are a substance,
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a chemical that's released in one area of the body,
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typically from something we call a gland,
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although they can also be released from neurons,
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but they're released often from glands
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that travel and have effects both on that gland,
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but also on other organs and tissues in the body.
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And that differentiates hormones
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from things like neurotransmitters,
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which tend to act more locally.
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So that's important.
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A hormone is a substance secreted at one location,
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the body travels and has impact
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on things elsewhere in the body.
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Examples of tissues that produce hormones
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would be the thyroid, the testes, the ovaries, et cetera.
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And then of course there are areas of the brain
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like the hypothalamus and the pituitary,
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which are closely related to one another
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and release hormones that cause the release
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of yet other hormones out in the body.
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So we're going to cover all this.
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If you don't know anything about endocrinology,
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you're still going to be able to understand
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today's discussion.
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And we're going to start with a discussion
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about what hormones actually do to create this thing
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that we call masculinization or feminization.
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So let's start with development.
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Everything that happens before that
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is a topic of the next episode.
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But sperm meets egg, this is mammalian reproduction.
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And that egg starts to duplicate.
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It starts to make more of itself.
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It makes more cells.
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And eventually some of those cells become skin.
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Some of those cells become brain.
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Some of those cells become muscle.
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Some of those cells become fingers.
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All the stuff that makes up the brain and body plan.
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In addition, there are hormones that come both
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from the mother and from the developing baby,
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the developing fetus that impact
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whether or not the brain will be
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what they call organized masculine or organized feminine.
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And as I say this,
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I want you to try and discard
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with the cultural connotations
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or your psychological connotations
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of what masculinization and feminization are
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because we're only centering on the biology.
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So typically people have either two X chromosomes
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and the traditional language around that
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is that person is female, right?
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Or an X chromosome and a Y chromosome
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and that person will become male.
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Now it's not always the case.
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There are cases where it's XXY
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where there are two X chromosomes plus a Y chromosome.
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There are also cases where it's XYY
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where there are two Y chromosomes
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and these have important biological
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and psychological impacts.
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So the first thing we need to establish
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is that there is something called chromosomal sex.
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Whether or not there are two X chromosomes
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or an X and Y chromosome is what we call chromosomal sex.
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But the next stage of separating out the sexes
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is what we call gonadal sex.
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Typically, not always,
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but typically if somebody has testes for their gonads
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we think of them as male.
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And if somebody has ovaries, we think of them as female.
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Although that's not always the case either
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but let's just explore the transition
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from chromosomal sex to gonadal sex
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because it's a fascinating one
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that we all went through in some form or another.
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So this XY that we typically think of
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as promoting masculinization of the fetus.
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We say that because on the Y chromosome, there are genes
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and those genes have particular functions
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that suppress female reproductive organs.
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So on the Y chromosome, there's a gene
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which encodes for something called
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a Mullerian inhibiting hormone.
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So there's actually a hormone
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that's programmed by the Y chromosome
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that inhibits the formation of Mullerian ducts
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which are an important part
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of the female reproductive apparatus.
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That's critical because already we're seeing the transition
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between chromosome Y chromosome and gonad.
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And other genes on the Y chromosome
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promote the formation of testes.
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So there are genes like the SRY gene
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and other genes that promote the formation of testes
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while they also inhibit the formation of the Mullerian ducts.
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So the transition from chromosomal sex to gonadal sex
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is a very important distinction.
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It's kind of a fork in the road
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that happens very early in development
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while fetuses are still in the embryo.
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Now, what's interesting as well
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is that just because there's a Y chromosome
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that can suppress Mullerian duct formation
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and there are other genes on the Y chromosome
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that promote teste development,
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the placenta itself is an endocrine organ.
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I think most people don't know this
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but the placenta is an endocrine organ.
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As well, the mother, which of course is carrying the fetus,
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has an adrenal gland which can produce testosterone.
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There are instances, for example,
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where a mother has either a tumor
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or for some other reason is secreting large levels
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of testosterone while carrying a fetus that is XX
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and that leads to what we would call masculinization
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of certain aspects of the fetus.
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Typically, that would be enlarged clitoris.
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There are also some examples of other phenotypes on the body
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that are created even though
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it's a purely XX chromosomal baby.
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So we have to distinguish
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between chromosomal sex, gonadal sex,
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and then there's what we call hormonal sex
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which is the effects of the steroid hormones,
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estrogen and testosterone and their derivatives
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on what we call morphological sex
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or the shape of the baby and the human and the genitalia
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and the jaw and all these other things.
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And so it actually is quite complicated.
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So it's a long distance from chromosomes to gender identity
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and gender identity has a lot of social influences and roles.
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This is an area that right now is very dynamic
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and in the discussion out there, as you know,
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but just getting from chromosomal sex
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to what we would call gonadal sex
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and hormonal sex and morphological sex
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involves a number of steps.
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So today we're going to talk about those steps
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and there's some fascinating things
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that do indeed relate to tools,
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do indeed relate to some important behavioral choices,
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important choices about things to avoid while pregnant.
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And for those of you that are not pregnant,
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things to avoid if you're thinking
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about eventually having children
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and that is not to drive development
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in one direction or another,
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but there are examples where there are some deleterious
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things in our environment
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that can actually negatively impact
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what we call sexual development overall,
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regardless of chromosomal background.
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So let's get started with that.
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Let's talk a little bit more about what hormones do.
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Hormones generally have two categories of effects.
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They can either be very fast or they can be very slow.
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There are hormones like cortisol and adrenaline,
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which act very fast.
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Adrenaline can increase your heart rate very fast
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when it's secreted into the body.
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Cortisol can be a little bit slower,
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but it also can have some very fast effects.
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And then there are hormones like testosterone and estrogen,
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which we refer to as the sex steroid hormones.
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The sex steroid hormones can have quick effects
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through signaling, meaning they can attach to cells
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and make those cells do different things.
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They can have actually quite quick effects on the brain.
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A lot of people don't know this,
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but there are some very fast effects
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of estrogen and testosterone, as well as long-term effects.
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These molecules, for those of you that are interested,
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are what are called lipophilic,
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which just means that they like fatty stuff.
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They can actually pass through fatty membranes.
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And because the outside of cells,
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as well as what's called the nuclear envelope,
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where all the DNA contents and stuff are stuffed inside,
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are made of lipid, of fat,
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these steroid hormones can actually travel into cells
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and then get into the,
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basically interact with the DNA of cells
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in order to control gene expression.
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So they can change the sorts of things
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that cells will become,
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and they can change the way that cells function
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in a long-term way.
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And that's actually how the presence of these genes,
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like SRY and molarion-inhibiting hormone,
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lead to reductions or elimination, I should say,
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of things like the molarion ducts
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and promote instead what's called in males,
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the Wolfian ducts,
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or promote the development of testes rather than ovaries.
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So all you need to know is that hormones have short-term
link |
and long-term effects,
link |
and the long-term effects are actually related
link |
to their effects on genes
link |
and how those genes are expressed or repressed
link |
in order to prevent them
link |
from having particular proteins made.
link |
So these hormones, these steroid hormones,
link |
are exceedingly powerful.
link |
And if we're going to have a discussion
link |
about masculinization or feminization, et cetera,
link |
you also need to think about the counterpart.
link |
It's not just about masculinizing the body
link |
or feminizing the body and brain,
link |
it's also about demasculinizing the brain in many cases
link |
as a normal biological function
link |
of typically of XX females,
link |
and defeminization, the suppression of certain pathways
link |
that are related to feminization of the body and brain.
link |
But there are some really fascinating twists in this story.
link |
So I've just thrown a lot of biology at you,
link |
but this is where it all starts to get incredibly surprising.
link |
You would think that it's straightforward, right?
link |
You have a Y chromosome,
link |
you suppress the female reproductive pathway
link |
like the malaria ducts,
link |
you promote the development of testes,
link |
and then testes make testosterone,
link |
and then it organizes the brain male,
link |
and it wants to do male-like things,
link |
and then in females, you get estrogen,
link |
and it wants to do female-like things,
link |
and air quotes here for all of this.
link |
And it turns out that isn't how it works at all.
link |
Here's where it's interesting.
link |
We have to understand that there are effects
link |
of these hormones, testosterone and estrogen,
link |
on what are called primary sexual characteristics,
link |
which are the ones that you're born with,
link |
secondary sexual characteristics,
link |
which are the ones that show up in puberty,
link |
and these are happening in the brain,
link |
and body, and spinal cord.
link |
And so I'm going to disentangle all this for you
link |
by giving you some examples.
link |
First, let's talk about the development
link |
of primary sexual characteristics,
link |
the ones that show up at birth.
link |
And one of the more dramatic examples of this
link |
comes from the role of testosterone
link |
in creating the external genitalia.
link |
Now, you might think it's just straightforward.
link |
If there's testes, because there's a Y chromosome,
link |
you've got a gene that codes for the development of testes,
link |
you get testosterone, and the penis grows,
link |
and the baby is born with a penis.
link |
One of the first things that happens
link |
when the baby comes out is they look at the genitalia,
link |
and they try and make an assessment
link |
on whether or not it's a, quote, boy,
link |
or it's a, quote, girl, right?
link |
That's been done for a very long time
link |
throughout human history.
link |
It turns out that it's not testosterone
link |
that's responsible for the development of the penis
link |
in a baby that has an X chromosome and a Y chromosome.
link |
It's a different androgen.
link |
Androgen is just a category of hormones
link |
that includes testosterone,
link |
but testosterone is converted in the fetus
link |
to something called dihydrotestosterone,
link |
and that's accomplished through an enzyme
link |
called 5-alpha reductase.
link |
Now, dihydrotestosterone has important effects
link |
later in life too.
link |
We will talk about those.
link |
In fact, if you just want to know,
link |
dihydrotestosterone is what we would call
link |
the dominant androgen in males.
link |
It's responsible for aggression.
link |
It's responsible for a lot of muscular strength.
link |
It's involved in beard growth and male pattern baldness.
link |
We're going to talk about all of that.
link |
But dihydrotestosterone has powerful effects
link |
in determining the genitalia
link |
while the baby is still in the embryo.
link |
So this ends, there's testosterone that's made,
link |
and that testosterone gets converted
link |
by this enzyme, 5-alpha reductase,
link |
in a little structure called the tubercle.
link |
That tubercle will eventually become the penis.
link |
So you say, okay, straightforward.
link |
This testosterone's converted to dihydrotestosterone,
link |
and then if there's dihydrotestosterone,
link |
it controls penis growth.
link |
And indeed, that's the case.
link |
So that's a primary sexual characteristic.
link |
That baby will then grow up, and later, during puberty,
link |
there will be the release of a molecule,
link |
I talked about this last episode,
link |
called kispeptin, K-I-S-S-P-E-P-T-I-N, kispeptin,
link |
which will cause the release of some other hormones,
link |
canadotropin-releasing hormone, luteinizing hormone,
link |
will stimulate the testes to make testosterone.
link |
So in puberty, testosterone leads to further growth
link |
and development of the penis,
link |
as well as the accumulation or growth of pubic hair,
link |
deepening of the voice,
link |
all the secondary sexual characteristics, okay?
link |
So dihydrotestosterone creates what we would call
link |
the typical masculine phenotype
link |
for primary sexual characteristics,
link |
and produces, testosterone, excuse me,
link |
produces secondary sexual characteristics during puberty.
link |
There's a very interesting phenomenon
link |
that was published in the journal Science in the 1970s,
link |
for which now there's a wealth of scientific data.
link |
And this relates to a genetic mutation
link |
where 5-alpha reductase,
link |
the enzyme that converts testosterone
link |
to dihydrotestosterone, doesn't exist.
link |
It's mutated in a way in a genome that it doesn't exist.
link |
And this actually was first identified
link |
in the Dominican Republic.
link |
It has shown up elsewhere.
link |
It's quite rare, but where it shows up, it's robust.
link |
What happens is baby is born.
link |
Typically, when a baby is born,
link |
they don't measure chromosomes.
link |
They don't look at chromosomal sex, XX or XY.
link |
That's not typically done nowadays.
link |
If you were to look at that baby, it would look female.
link |
There would be very little or no external penis.
link |
And so people would say, it's a girl,
link |
and they might have the celebration, it's a girl.
link |
And I guess now they call them gender reveal parties
link |
or something like that.
link |
I don't know about this.
link |
But anyway, the baby would reveal its external genitalia
link |
simply by being there and being naked when it's born.
link |
Has nothing to do with gender.
link |
It has to do with genitalia and sex.
link |
That baby would be born.
link |
And what was observed is that from time to time,
link |
that baby, after being raised as a girl,
link |
perfectly happy as a girl,
link |
would, around the age of 11 or 12 or 13,
link |
would suddenly start to sprout a penis.
link |
There's actually a name for this.
link |
It's called huevidosis,
link |
which the translation is more or less penis at 12.
link |
And as strange as this might sound,
link |
it makes sense if you understand the underlying mutation.
link |
What happens in these children, these huevidosis,
link |
is that the child is born.
link |
It has testes, which are not descended, so up in the body.
link |
They're not making a lot of testosterone early on.
link |
They weren't able to convert testosterone
link |
to dihydrotestosterone
link |
because they lack this enzyme, 5-alpha reductase.
link |
As a consequence, the primary sexual characteristic
link |
of external male genitalia, penis, doesn't develop.
link |
And then what happens is the baby grows up
link |
as a young child, essentially as treated as a girl.
link |
Generally, they report being pretty comfortable as girls,
link |
although not always.
link |
And then testosterone starts getting secreted
link |
from the testes because kispeptin in the brain
link |
signals through gonadotropin and luteinizing hormone,
link |
travels down to the testes.
link |
The testes start churning out testosterone
link |
and there's a secondary growth of the penis.
link |
And all of a sudden there's a penis.
link |
And this leads to some very complicated situations
link |
in families and culturally.
link |
And actually the outcomes in terms of whether or not
link |
these children decide to self-identify as males or females
link |
and how people treat them actually varies quite a lot.
link |
There's actually been a kind of an adopting
link |
of a third category of sex and gender in the suavodosis
link |
in order to just offer them the opportunity
link |
to explore not just what would be a typical kind of girl
link |
or woman or boy or man phenotype, but something in between,
link |
something that some people call intersex,
link |
although intersex and pseudohermaphroditism
link |
is actually a separate thing altogether.
link |
So it's fascinating.
link |
And the point here is that dihydrotestosterone,
link |
not testosterone is responsible for this primary growth
link |
of the penis and that testosterone later is involved
link |
in the secondary sexual characteristics,
link |
deepening in the voice, et cetera.
link |
Now, this is where the information gets even more
link |
interesting and applies to essentially everybody.
link |
You might think that testosterone,
link |
because it masculinizes the body
link |
in the secondary sexual characteristic way
link |
and because dihydrotestosterone, another androgen,
link |
masculinizes the primary sexual characteristics,
link |
the growth of the penis early on,
link |
that testosterone must masculinize the brain.
link |
And there are in fact aspects of masculinization
link |
of the brain and body that are independent of genitalia.
link |
Now it might be obvious to some of you,
link |
but some people probably don't realize that.
link |
Yes, indeed, the brain has receptors for testosterone.
link |
It also has receptors for estrogen.
link |
But the fascinating thing is that if you look at the brains
link |
of people that have Y chromosomes
link |
and that have testes and that make testosterone,
link |
and you look at the brains of people
link |
that don't have Y chromosomes or testes
link |
and therefore make far less testosterone in general,
link |
what you realize is that the cells in the brain
link |
that differ between what I'll call males and females,
link |
but between XY and XX have receptors for testosterone,
link |
but the masculinization of the brain
link |
is not accomplished by testosterone.
link |
I want to repeat this.
link |
The masculinization of the brain
link |
is not accomplished by testosterone.
link |
It is accomplished by estrogen.
link |
Testosterone can be converted into estrogen
link |
by an enzyme called aromatase.
link |
This is vitally important to understand.
link |
Testosterone can be converted into estrogen
link |
by something called aromatase.
link |
I'll give an example of where this happens later in life
link |
to just illustrate the principle
link |
and really embedded in your mind.
link |
During puberty in boys, XY chromosome individuals,
link |
it's not uncommon for there to be transient
link |
or sometimes long lasting breast bud development.
link |
Testosterone goes up during puberty
link |
for the reasons we talked about before,
link |
and some of that testosterone gets converted into estrogen
link |
by an enzyme called aromatase.
link |
Aromatase is made by several sources in the body.
link |
One of the main sources is body fat.
link |
So it can make a lot of aromatase.
link |
Sometimes you'll even see a fairly dramatic
link |
breast development in males during puberty.
link |
Sometimes it's transient, sometimes it's not.
link |
The other place where you see this
link |
is in athletes and bodybuilders
link |
that take a lot of anabolic steroids
link |
that take high levels of androgens.
link |
So they'll be taking testosterone
link |
at super physiological doses.
link |
Sometimes not always,
link |
they will convert some of that testosterone into estrogen
link |
and they'll get what's called gynecomastia,
link |
which is the development of male breast tissue.
link |
Sometimes they'll get it cut out surgically.
link |
Other times they'll start trying to take estrogen blockers
link |
in order to try and suppress it,
link |
or they'll try and block prolactin.
link |
It's a topic that we're going to get into in more detail,
link |
but what's important here is to understand
link |
that testosterone can be converted
link |
into the estrogen by aromatase.
link |
Aromatase is not just made in body fat.
link |
There are neurons in the brain that make aromatase
link |
and convert testosterone into estrogen,
link |
and it is testosterone converted into estrogen.
link |
In other words, it's estrogen
link |
that masculinizes the XY individual,
link |
that masculinizes the brain.
link |
And this has profound effects on all sorts of things,
link |
on behavior, on outlook in the world, et cetera.
link |
But I think most people don't realize
link |
that it's estrogen that comes from testosterone
link |
that masculinizes the male brain, the XY brain,
link |
not testosterone nor dihydrotestosterone.
link |
So I just want to mention some tools.
link |
You might be asking yourself,
link |
how could tools possibly come up
link |
at this stage of the conversation
link |
where we're talking about sexual development
link |
and we're talking about the differentiation
link |
of tissues in the body?
link |
Well, this is true both for children and parents and adults.
link |
I want to emphasize that there are things
link |
that are environmental and there are things that people use
link |
that in their homes sometimes
link |
that actually can impact hormone levels
link |
and can impact sexual development in fairly profound ways.
link |
And I want to be very clear.
link |
This is not me pulling from some rare journal
link |
I've never heard of it.
link |
This is pulling from textbooks.
link |
In particular, today, I'm guiding a lot of the conversation
link |
on work on behavioral endocrinology.
link |
This is a book by Randy Nelson and Lance Crigfield,
link |
true experts in the field.
link |
I'm going to talk about some of the work from Tyrone Hayes
link |
from UC Berkeley about environmental toxins
link |
and their impacts on some of these things
link |
like testosterone and estrogen.
link |
I'm going to touch into them.
link |
I'm going to give some anecdotal evidence
link |
that's grounded in studies,
link |
which we will provide in the caption
link |
or that I'll reference here.
link |
One of those that's actually really interesting
link |
but helps illustrate the principle
link |
that we've been talking about is a few years ago,
link |
there was a lot of excitement about evening primrose oil.
link |
Evening primrose oil is in a lot of products
link |
that typically are associated with skin beauty
link |
And so I'm generalizing here,
link |
but typically it was mothers or sisters that were using it.
link |
And there were actually examples starting to crop up
link |
of young boys getting accelerated breast bud development
link |
from skin contact with women
link |
who were using evening primrose oil.
link |
So evening primrose oil is chemically a lot like estrogen
link |
and it has a lot of estrogenic compounds.
link |
There are a number of things out there like this.
link |
So believe it or not, things like pine pollen
link |
look very much like testosterone.
link |
Structurally, they are more or less are testosterone.
link |
Their bioavailability in humans isn't as clear.
link |
Evening primrose oil has a lot of estrogenic elements to it,
link |
just structurally how it's built.
link |
And so there were cases where boys were understandably
link |
being hugged by their mom or maybe even like showering
link |
and taking a, using the evening primrose oil solution.
link |
Those things will actually change levels of estrogens
link |
in boys and girls.
link |
And so this wasn't just an issue for young boys.
link |
This was also an issue for young girls.
link |
So it's not that evening primrose oil is bad.
link |
It's just that many of you have probably heard
link |
about the dangers of soy and isoflavones
link |
and things like that.
link |
The impact of soy on estrogen levels
link |
is there are some decent evidence to support that.
link |
However, there's a lot of other factors
link |
that are more severe.
link |
And one of those is this evening primrose oil.
link |
So regardless of age, let's just put it this way
link |
because people might be wanting to drive their hormones
link |
more estrogenic or more androgenic.
link |
How could I know what your preference is?
link |
But in any case, things like evening primrose oil
link |
can actually promote estrogenic pathways in the body
link |
and some of it can go transdermal.
link |
Likewise, because testosterone replacement therapy
link |
is fairly widespread nowadays
link |
and some people accomplish that through cream,
link |
it's pretty well understood that if someone's taking that,
link |
that they want to avoid contact with anyone,
link |
skin contact with anyone that is trying to promote
link |
more estrogenic activity in their body
link |
and especially in children.
link |
The other is this issue of environmental factors.
link |
Now this, again, I'm just going to highlight
link |
when one starts talking about environmental factors
link |
and how they're poisoning us or disrupting growth
link |
or fertility rates,
link |
it can start to sound a little bit crazy
link |
except when you start to actually look
link |
at some of the real data,
link |
data from quality research labs
link |
funded by federal government,
link |
funded not from companies or other sources
link |
that are really aimed at understanding
link |
what the underlying biology is.
link |
And for that, we should all be grateful
link |
to Tyrone Hayes at UC Berkeley.
link |
I remember way back when I was a graduate student
link |
in the late 90s, goodness, at UC Berkeley.
link |
And I remember him, he was studying frogs.
link |
He was talking about developmental defects
link |
in these frogs that live in different waters around,
link |
it was California, but also elsewhere.
link |
And he identified a substance which is present
link |
in a lot of waterways throughout this country
link |
and other countries, so US and beyond,
link |
certainly not just restricted to California,
link |
which is atrazine, this is A-T-R-A-Z-I-N-E.
link |
Again, this is the stuff of textbooks
link |
and it causes severe testicular malformations.
link |
So again, atrazine exposure is serious.
link |
And what's interesting is if you look at the data,
link |
what you find is that at sites in Western
link |
and Midwestern sections of the United States,
link |
10 to 92% of male frogs, these were frogs mind you,
link |
had testicular abnormalities.
link |
And the most severe testicular malformations
link |
were in the testes rather than in the sperm.
link |
So it's actually the organ itself, the gonad itself.
link |
Now, it's very well known now that atrazine
link |
is in many herbicides.
link |
And so, whereas I would say in the 80s and 90s,
link |
the discussion around herbicides and their negative effects
link |
was considered kind of like hippie dippie stuff
link |
or the stuff you hear about it,
link |
your local community markets
link |
and these kind of new age communities,
link |
now there's very solid data from federally funded labs
link |
at major universities that have been peer reviewed
link |
and published in excellent journals,
link |
showing that indeed many of these herbicides
link |
can have negative effects primarily by impacting
link |
the ratios of these hormones in either the mothers
link |
or in the testes, altering the testes of the fathers
link |
or direct effects on developing young animals
link |
and potentially humans.
link |
And so you ask, well, what about humans?
link |
Frogs are wonderful, but what about humans?
link |
So here are the data on what's happening.
link |
And this isn't all going to be scary stuff.
link |
We're also going to talk about tools to ameliorate
link |
and offset some of these effects.
link |
One would be be cautious with evening primrose
link |
as well as testosterone creams,
link |
depending on whether or not you want to be more androgenic
link |
or estrogenic, depending on your needs.
link |
But across human populations,
link |
sperm counts are indeed declining, okay?
link |
So in 1940, the average density of human sperm
link |
was 113 million per milliliter of semen.
link |
That's how it's measured.
link |
How many sperm per milliliter of semen?
link |
In 1990, this figure has dropped to 66.
link |
It went from 113 million per milliliter
link |
to 66 million per milliliter in the United States
link |
and Western Europe.
link |
So it's not just a US thing.
link |
Researchers also estimated that the volume of semen
link |
produced by men has dropped 20% in that time,
link |
reduced sperm count per ejaculation even further.
link |
So between 1981 and 1991,
link |
the ratio of normal spermatogenesis has decreased
link |
from 56.4% to 26.9%.
link |
So there's a lot that's happening,
link |
primarily because of these herbicides
link |
that are in widespread use to reduce sperm counts.
link |
And these are going to have profound effects,
link |
not just on sperm counts, but on development,
link |
sexual development at the level of the gonads and the brain,
link |
because you need testosterone to get you
link |
dihydrotestosterone for primary sexual characteristics.
link |
You need estrogen that's come from testosterone
link |
to masculinize the brain.
link |
And of course, we're not just focusing on sperm
link |
You of course also know that many of these herbicides
link |
are disrupting estrogens in a similar way,
link |
or are leading to hyper estrogenic states,
link |
which might explain why puberty is happening
link |
so much earlier in young girls these days.
link |
So there are a lot of things that are happening.
link |
Now, does this mean that you have to run around
link |
and neurotically avoid anything that includes
link |
things like atrazine,
link |
and should you be avoiding all kinds of herbicides?
link |
I don't know, that's up to you,
link |
but it does seem that these have pretty marked effects
link |
in both the animal studies and in the human studies.
link |
You can open up a textbook like the endocrinology textbook
link |
and find things like vinclozolin.
link |
This is V-I-N-C-L-O-Z-O-L-I-N,
link |
which is a fungicide and it's an anti-androgen.
link |
You give it to animals, to rats,
link |
and instead of forming a penis, they don't form a penis.
link |
They basically, it's not that they form a clitoris,
link |
they just don't form a penis.
link |
So let's talk about female sexual development.
link |
what we'll do is we'll talk about the normal biology.
link |
Then we'll talk a little bit about a kind of extraordinary
link |
or unusual set of cases,
link |
but we'll talk about them
link |
because they illustrate an important principle
link |
about how things work under typical circumstances.
link |
So there is a mutation
link |
called androgen insensitivity syndrome.
link |
And understanding how androgen insensitivity syndrome works
link |
can help you really understand
link |
how hormones impact sexual development.
link |
So here's how it works.
link |
There are individuals who are XY,
link |
so they have a Y chromosome,
link |
that are born, that make testosterone,
link |
they have testes, and they don't have molarion ducts
link |
because on the Y chromosome
link |
is this molarion inhibiting hormone.
link |
However, these individuals look completely female.
link |
And in general, they report feeling
link |
like girls when they're young, women when they're older.
link |
But there's something unusual that's happening
link |
in these individuals
link |
because they have an XY chromosomal type and not XX.
link |
So what's happening?
link |
Well, what's happening is
link |
the testes are making testosterone,
link |
but the receptor for testosterone is mutated.
link |
And therefore, the testes never descend.
link |
They don't have ovaries, they have testes,
link |
but the testes are internal.
link |
And so typically, these individuals find out
link |
that they are actually XY chromosomes
link |
so that their chromosomal sex is male, if you will,
link |
and their gonadal sex is male,
link |
but the gonads, the testes are inside the body,
link |
they don't actually develop a scrotum,
link |
they don't make ovaries,
link |
and when they don't menstruate around the time of puberty,
link |
that's a sign that something is different.
link |
And so they never menstruate around puberty,
link |
and if they look into this deeply enough,
link |
what you find is that they are actually XY,
link |
they make testosterone,
link |
but their body can't make use of the testosterone
link |
because they don't have the receptors.
link |
And the receptors are vitally important
link |
for most all of the secondary sexual characteristics
link |
that we talked about,
link |
body hair, penis growth during puberty, et cetera.
link |
They live fairly happy lives as females,
link |
although, of course, they can't conceive, right?
link |
They don't have a uterus, they don't have ovaries.
link |
They also, in general, don't produce sperm
link |
in quantities enough
link |
that they could actually reproduce with somebody else,
link |
although sometimes they can.
link |
And believe it or not, and I'm not going to name names,
link |
but there are actually reports of several people,
link |
fairly prominent people throughout history,
link |
who have had this androgen insensitivity syndrome,
link |
or people suspected they did.
link |
And the reason to not name names
link |
is that it gets right to the heart
link |
of whether or not they are male or female.
link |
How could you say, right?
link |
They have XY chromosomes,
link |
but gonadally, they have testes that are inside.
link |
And yet, if you looked at their bodies,
link |
if you looked at their faces,
link |
you would say, almost with certainty,
link |
that they appeared female.
link |
And that naturally occurring experiment
link |
points to the fact that testosterone
link |
that shows up in the body
link |
and impacts the things at the levels of the receptor
link |
has a profound effect on phenotype,
link |
on the external or body plan.
link |
So again, we're talking about this
link |
in order to illustrate the principle
link |
that in order to have its effects,
link |
a hormone doesn't just have to be present,
link |
that hormone actually has to be able to bind its receptor
link |
and take action on the target cells.
link |
And once again, I'll just throw out the example
link |
of where people are using performance-enhancing drugs,
link |
although that's a pretty broad statement.
link |
Nowadays, there's a lot of excitement
link |
about the so-called SARMs,
link |
which are more on the receptor side.
link |
And so we'll talk about this in a future episode.
link |
And I just say that as a teaser
link |
because the SARMs and what's happening right now
link |
in augmenting sports performance,
link |
both with testosterone directly,
link |
but also testosterone derivatives,
link |
and then also altering things at the level of the receptor
link |
is exceedingly interesting
link |
and is revealing to us the many ways
link |
in which hormones can impact brain and body in ways
link |
that we didn't suspect.
link |
Perhaps the simplest way to understand
link |
how estrogen and testosterone impact masculinization
link |
or feminization of the brain and behavior
link |
is from a statement.
link |
It's actually the closing sentence of an abstract
link |
that my colleague Narao Shah
link |
at Stanford School of Medicine published,
link |
which is that estrogen,
link |
again, it's estrogen that is aromatized from testosterone
link |
by aromatase, sets up the masculine repertoire of sexual
link |
and in animals and in humans, territorial behaviors.
link |
So it sets up the circuitry in the brain.
link |
Estrogen does that.
link |
Estrogen sets up the masculine circuitry in the brain.
link |
And testosterone is then what controls the display
link |
of those behaviors later in life.
link |
And I find that incredibly interesting.
link |
You would think it was just testosterone did one thing
link |
and estrogen did another,
link |
but it turns out that nature
link |
is far more interesting than that.
link |
Okay, so what are some things
link |
that impact sexual development early in life
link |
and later in life?
link |
Let's talk about cannabis.
link |
Let's talk about alcohol.
link |
And dare I say, let's talk about cell phones.
link |
Something that I never thought I would ever do
link |
either in this podcast or in the classroom,
link |
but these days there are really interesting data
link |
and I think you should be aware of them.
link |
First of all, cannabis, marijuana, THC.
link |
I realize that there are now
link |
a lot of different variants on this.
link |
There are a lot of different strains of cannabis.
link |
I personally am not a pot smoker.
link |
It's just not for me.
link |
I'm not talking about the moral or legal implications.
link |
In some states it's decriminalized,
link |
in other places it's really illegal,
link |
in other places it's basically legal.
link |
You have to check where you live and understand the laws.
link |
That's not what this is about.
link |
What we do know, however,
link |
is that with the exception of one study,
link |
there are many studies that point to the fact
link |
that THC and other things in cannabis
link |
promote significant increases in aromatase activity.
link |
Pot smokers aren't going to like this,
link |
especially male pot smokers aren't going to like this,
link |
but it's the reality.
link |
Remember, what you're hearing in the background
link |
is Costello snoring really loud.
link |
Should we put him on screen?
link |
He's not a cannabis smoker, but you can imagine why.
link |
Here, come here Costello, come here buddy, come here.
link |
He's asleep, come here.
link |
He's like, come here.
link |
This dog definitely does not need cannabis.
link |
This is his state for most of the time.
link |
He is highly, apparently he's asleep still.
link |
So some of you have asked to see Costello.
link |
If you're just listening on audio,
link |
maybe he'll give us something.
link |
That's a, oh, okay.
link |
We're going to let him get back to sleep.
link |
Some of you have asked to see him.
link |
Costello is not a pot smoker either.
link |
He did have a dog sitter that was a pot smoker years ago.
link |
It was his favorite dog sitter, but I'm not a pot smoker.
link |
Again, no judgment, but here's the deal.
link |
That cannabis, and it's not clear if it's THC itself
link |
or other elements in the marijuana plant,
link |
promote aromatase activity.
link |
Now, this has been observed anecdotally
link |
where pot smokers have a higher incidence
link |
of developing something I mentioned before,
link |
gynecomastia, breast bud development,
link |
or full-blown breast development in males.
link |
There may be some women
link |
who want to increase their estrogenic activity.
link |
Remember, females make testosterone.
link |
It comes from the adrenals, right?
link |
They don't have testes, so it comes from the adrenals,
link |
and that testosterone can also be aromatized,
link |
although typically most of the aromatase activity
link |
that we're referring to in these examples is in males.
link |
So testosterone can increase estrogenic activity.
link |
So you might say, oh, therefore,
link |
does testosterone reduce sexual behavior?
link |
Does it create all sorts of things
link |
that are related to low testosterone?
link |
Not necessarily, not necessarily, and here's why.
link |
Estrogen itself in males and females
link |
is important for things like libido and sexual behavior.
link |
I'm going to repeat that.
link |
If estrogen is too low in males,
link |
it can actually inhibit libido and sexual behavior.
link |
So you don't want estrogen too high or too low,
link |
whether or not you're male or female.
link |
Now, of course, in females,
link |
estrogen levels tend to be higher than in males.
link |
I'm speaking very generally here.
link |
You just think back to the chromosomal sex.
link |
That's what I'm referring to when I say male or female,
link |
although there's nuance there, of course.
link |
In females, the testosterone that comes from the adrenals
link |
has a powerful effect on libido and desire to reproduce,
link |
and in the next episode,
link |
we're going to talk about how that works
link |
in its relationship to birth control,
link |
its relationship to menopause.
link |
We're also going to talk about how that whole thing works
link |
But cannabis and other aspects of the marijuana plant
link |
can impact levels of testosterone and estrogen
link |
by increasing aromatase,
link |
and so people should be aware of that.
link |
As well, there are good data.
link |
I was able to find several studies on PubMed
link |
pointing to the fact that smoking marijuana
link |
during pregnancy can shift the pattern of hormones
link |
in the developing fetus,
link |
such that it promotes more estrogenic outcomes.
link |
Now, earlier I said that estrogen
link |
is what masculinizes the male brain.
link |
In utero, that's true,
link |
but the way that cannabis seems to work,
link |
at least from the studies I was able to identify,
link |
is that it promotes circulating estrogen in the body
link |
and therefore can counteract
link |
some of the masculinizing effects
link |
of things like testosterone and dihydrotestosterone
link |
on primary and secondary sexual characteristics.
link |
So I mention this because, you know,
link |
I think nowadays marijuana use is far more widespread
link |
and certainly during puberty,
link |
it can have profound effects on these hormonal systems.
link |
And so we'll do another episode
link |
that goes really deep into this,
link |
but yes, cannabis promotes estrogenic activity
link |
by increasing aromatase.
link |
Most everyone can appreciate that drinking during pregnancy
link |
is not good for the developing fetus.
link |
Fetal alcohol syndrome is a well-established
link |
negative outcome of pregnancy.
link |
And it's something that there are cognitive effects
link |
that are really bad.
link |
There's actually physical malformation, et cetera.
link |
So drinking during pregnancy, not good.
link |
Probably drinking during puberty, not good either
link |
because alcohol, in particular, certain things like beer,
link |
but other grain alcohols can increase estrogenic activity.
link |
Now, this isn't just about protecting young boys
link |
from estrogenic activity.
link |
It's also protecting girls from excessive
link |
or even hypoestrogenic effects of alcohol in puberty.
link |
Now, many teenagers drink, college students drink,
link |
and it's important to point out that puberty
link |
doesn't start on one day and end on another day.
link |
Puberty has a beginning, a middle, and an end.
link |
But development is really our entire lifespan.
link |
This idea that puberty has us open and close,
link |
that's just false.
link |
Okay, so we talked about cannabis.
link |
We talked about alcohol.
link |
Let's talk about cell phones.
link |
First of all, I use a cell phone.
link |
I use it very often,
link |
and I do not think they are evil devices.
link |
I think that they require some discipline
link |
in order to make sure that it does not become
link |
a negative force in one's life.
link |
So I personally restrict the number of hours
link |
that I'm on the phone and in particular on social media.
link |
I only answer email at particular times of day.
link |
But what about the cell phone itself?
link |
When I was a junior professor,
link |
I was a pre-tenure, early professor,
link |
I taught this class on neural circuits
link |
and health and disease.
link |
And one of the students asked me,
link |
are cell phones safe for the brain?
link |
And all the data pointed to the fact that they were,
link |
or at least there were no data showing that it wasn't.
link |
I still don't have the answer on that, frankly.
link |
I don't see a lot of studies about it.
link |
I'm not personally aware of any evidence
link |
in quality peer-reviewed studies
link |
showing that cell phones are bad for the brain
link |
or that holding the phone to the ear is bad
link |
or that Bluetooth is bad or any of that.
link |
I'm just not aware of any quality studies.
link |
If you are aware of quality studies, peer-reviewed studies,
link |
please reference them, put them in the comment section,
link |
send them to me, however you like.
link |
I'd love to see them.
link |
I'm not aware of them.
link |
However, I was very interested in a particular study
link |
that was published back in 2013 on rats.
link |
It was basically took a cell phone
link |
and put it under a cage of rats
link |
and looked at basically testicular
link |
and ovarian development in rats
link |
and saw minor but still statistically significant defects
link |
in ovarian and testicular development.
link |
Since then, and now returning to the literature,
link |
I've seen a absolute explosion of studies,
link |
some of which are in quality journals,
link |
some of which are in what I would call
link |
not blue ribbon journals,
link |
identifying defects in testicular and or ovarian development
link |
by mere exposure to cell phone emitted waves.
link |
Let's just call that.
link |
We don't know what they are.
link |
And this sounds almost crazy, right?
link |
Anytime somebody starts talking about EMFs
link |
and things like that, you kind of worry like,
link |
is this person okay?
link |
But look, the literature are pointing in a direction
link |
where chronic exposure of the gonads to cell phones
link |
could be creating serious issues
link |
in terms of the health at the cellular level
link |
and in terms of the output.
link |
So the output for the testes would be sperm production.
link |
Swimming speed in sperm is an important feature
link |
of sperm health. In the ovaries,
link |
it would be estrogenic output,
link |
how regular the cycles are.
link |
So in animals, the cycles are a little bit different
link |
than in humans. They don't have a menstrual cycle.
link |
They have an estrous cycle,
link |
which is generally around four days.
link |
I think that it's fair to say based on the literature
link |
that there are effects of cell phone emitted waves
link |
on gonadal development.
link |
The question is, what is the proximity of the cell phone
link |
Now I've taken the literature as I observe it.
link |
And then of course, we'll point you to in the captions.
link |
And I don't like to have my cell phone on and in my pocket.
link |
I'm well past puberty, but nonetheless,
link |
some of these effects were seen in adult animals.
link |
There are effects now that have been demonstrated in humans.
link |
So let's just talk about a couple of those effects.
link |
So a paper published in the journal Clinical Biochemistry
link |
from Eskander et al, looked at hormone profiles
link |
in people based on proximity to their phone
link |
and frequency of phone use,
link |
where they stored their phone on their body,
link |
as well as proximity of where they lived to,
link |
I guess they're called these radio frequency towers,
link |
so the base stations.
link |
And they were looking at effects of radio frequency,
link |
radiation, RFR on human hormone profiles.
link |
And they show significant decreases in cortisol.
link |
You might say, well, that might be good,
link |
but you need that morning cortisol bump
link |
in order to wake up, morning cortisol is good.
link |
But also thyroid hormones were significantly reduced.
link |
Prolactin in young females, that's definitely concerning.
link |
And testosterone levels in males and females.
link |
And so there are now quite good data showing
link |
that being close to the phone too much of the day
link |
and how close is an interesting question,
link |
or living near one of these base stations
link |
apparently can have effects on hormone profiles.
link |
And when you see a study like this, one should always ask,
link |
well, what are the other things that could also have effects
link |
on these hormone profiles, right?
link |
Because you could imagine that if you ran the same study
link |
of people that live close to a waterway
link |
or close to a highway where there's a lot of exhaust
link |
from buses and cars, you might see similar effects.
link |
So you have to take these sorts of studies
link |
with a grain of salt.
link |
But I think it's very interesting.
link |
And given that the last time I looked into these data
link |
were way back when I was a junior professor
link |
and there was like one or two studies that I could find,
link |
one of the studies pointed to increases in testosterone
link |
in rats where they had close proximity
link |
to these radio frequency radiation waves.
link |
And then in the other case,
link |
it showed decreases in testosterone.
link |
So there really wasn't any conclusion to take away
link |
So now there's pretty impressive amount of data
link |
pointing to the fact that there are effects
link |
of these things on hormones.
link |
I don't know what to do with that information.
link |
I'm not going to stop using my phone,
link |
but in light of the work from Tyrone Hayes and others
link |
looking at sperm counts and looking at the decrease
link |
in testosterone levels and sperm counts and fertility
link |
over the last 20, 30 years,
link |
perhaps it's not surprising.
link |
Although there again, cell phones and smartphones
link |
have really been in prominent use
link |
mostly within the last 10 or 11 years.
link |
And so it's hard to explain all of those declines
link |
simply on the basis of cell phone use.
link |
There's some interesting effects of hormones
link |
that actually you can observe on the outside of people
link |
that tell you something about
link |
not just their level of hormones,
link |
but also about their underlying genetics.
link |
And these relate to beard growth and baldness.
link |
And it's fascinating.
link |
The molecule, the hormone,
link |
dihydrotestosterone made from testosterone
link |
is the hormone primarily responsible for facial hair,
link |
As well, it's the molecule,
link |
the hormone primarily responsible for lack of hair
link |
on the head for hair loss.
link |
So how does that work?
link |
Well, DHT circulates in the body
link |
and it binds to DHT receptors in the face
link |
to promote hair growth.
link |
But it binds to DHT receptors on the scalp
link |
to promote hair loss.
link |
the drugs that are designed to prevent hair loss
link |
are 5-alpha reductase inhibitors.
link |
So remember 5-alpha reductase from the huevadosis?
link |
Well, the people that discovered the huevadosis
link |
went on to do a lot of research
link |
on the underlying biochemistry
link |
of this really interesting molecule, dihydrotestosterone.
link |
They identified 5-alpha reductase
link |
and 5-alpha reductase inhibitors
link |
are the basis of most of the anti-hair loss treatments
link |
that are out there.
link |
And so there are some interesting things here.
link |
First of all, the side effect profiles
link |
of those treatments for hair loss
link |
are quite severe in many individuals.
link |
Remember DHT is the primary androgen for libido,
link |
for strength and connective tissue repair,
link |
even if that aggression of course is held in check,
link |
but just sort of ambition and aggression
link |
is related to dopamine,
link |
but within the testosterone pathway,
link |
less so pure testosterone,
link |
although pure testosterone has its effects,
link |
but DHT is at least in primate species including humans
link |
is the dominant androgen
link |
for most of those sorts of effects.
link |
And if you look at somebody,
link |
everyone can predict whether or not
link |
they're going to go bald based on looking at their,
link |
we're always taught our mother's father.
link |
So if your mother's father was bald,
link |
there's a higher probability that you're going to go bald.
link |
The pattern of DHT receptors on the scalp
link |
will dictate whether or not
link |
you're going to go bald everywhere
link |
or just in the front or so called crown type baldness.
link |
And the density of the beard
link |
tells you about the density of DHT receptors.
link |
Now this varies by background, by genetic background.
link |
And actually around the world nowadays,
link |
because people travel and people form couples
link |
and have kids with so many different people
link |
of different mixed cultures,
link |
you're seeing this starting to disappear.
link |
But there are areas of the world
link |
where all the men seem to be,
link |
have the same pattern of baldness,
link |
like a strip of baldness down the center
link |
with hair still on the sides and full beards.
link |
That's because these patterns of DHT receptors
link |
are genetically determined.
link |
Elsewhere, testosterone levels can still be very high.
link |
DHT levels in the blood can be very high.
link |
And yet people will have very light beards or no beards.
link |
And that's because they don't have
link |
a lot of DHT receptors in the face.
link |
And still other cultures,
link |
you'll see people with huge beards,
link |
tons of beard grow like their beards
link |
are growing all the way up to their eyes
link |
and they have huge heads of hair.
link |
And that's because they have a lot of DHT receptors
link |
on the face and not on the scalp.
link |
So there are a lot of effects of DHT
link |
that you can just see in male phenotypes.
link |
And it's interesting that these hair loss drugs
link |
that are, or to prevent hair loss drugs
link |
are directly aimed at preventing the conversion
link |
of testosterone into dihydrotestosterone.
link |
And that's why they, to some extent prevent hair loss,
link |
but also to some extent have a bunch of side effects
link |
that are associated with low DHT.
link |
Along these lines, there's a particular sports supplement
link |
that a lot of people use called creatine.
link |
Creatine now, there's a lot of research
link |
showing that creatine can bring more water into the muscle.
link |
It can support strength.
link |
It does a number of other things.
link |
Might even have some important cognitive promoting,
link |
cognitive enhancement effects, although mild.
link |
The studies there show that it can be significant.
link |
Some people, not all, it's more anecdotal,
link |
report that creatine promotes hair loss.
link |
It differs by individual.
link |
For some people that's true, for others, no.
link |
But yes, it does appear based on the studies
link |
I was able to find on PubMed
link |
that creatine does promote 5-alpha reductase activity
link |
and therefore the conversion of testosterone
link |
into dihydrotestosterone.
link |
And so it makes sense that it might promote
link |
some degree of hair loss, as well as beard growth,
link |
as well as the other effects of DHT.
link |
I recall in junior high school and middle school,
link |
going home one summer, it was seventh grade,
link |
coming back in the eighth grade,
link |
and a kid that I knew that I was friends with
link |
went from being like a young kid to,
link |
he was like a grown man, he had a full beard.
link |
It was like he would completely transform.
link |
I mean, puberty, as I've said before,
link |
is without a doubt the most accelerated
link |
rate of development that we will go through
link |
at any point in our lives, even faster than infancy,
link |
just in terms of the huge number
link |
of different cognitive changes and physical changes.
link |
Not surprisingly, that same individual
link |
was mostly or bald by his early 20s.
link |
And that's because he must've had
link |
just exceedingly high levels of DHT.
link |
I also played soccer with this kid,
link |
and he was basically like dribbling past everybody.
link |
He was like a grown man playing soccer
link |
with a bunch of little kids.
link |
Full beard, bald at 20.
link |
And so the rate of maturation,
link |
the rate of aging is very interesting.
link |
It's hard to know rate of aging.
link |
There's some genetic tests that now can allow you to do that.
link |
Things like Horvath clocks and things of that sort.
link |
Beautiful work of David Sinclair at Harvard
link |
and others has pointed to this.
link |
The speed of entry and exit from puberty might be,
link |
I'm putting it out there as a hypothesis,
link |
might be an interesting window
link |
into how fast one is going through
link |
their aging or developmental arc,
link |
because development, of course,
link |
doesn't just start at birth and end after puberty.
link |
It continues your entire life.
link |
So I think it's interesting.
link |
You will often see that people, boys and girls,
link |
I should say boys or girls,
link |
will develop secondary sexual characteristics
link |
at different rates.
link |
And sometimes it's sequential.
link |
You might see a kid will,
link |
she'll grow very tall or she'll have a big growth spurt,
link |
but then breast development will come a little bit later.
link |
And then other features will come a little bit later.
link |
You can also see this in boys.
link |
The person that I referred to earlier,
link |
my friend that developed full beard, went bald.
link |
He was also quite muscular.
link |
He's a great athlete.
link |
So he went through puberty exceedingly fast.
link |
Other people go through it more slowly.
link |
Some people will go through puberty at age 14,
link |
but they won't start to accumulate facial hair
link |
until much, much later.
link |
Or their voice will change first very early,
link |
and then they won't get the other secondary
link |
sexual characteristics until much later.
link |
And so we don't really know how that impacts
link |
or relates to overall trajectory or rate of aging,
link |
but it's an interesting thing to think about
link |
for each and every one of us.
link |
I'm going to offer you the opportunity
link |
to do an experiment today while listening to the podcast.
link |
But first I want to tell you a story about hyenas,
link |
professional baseball, and clitorises the size of penises.
link |
So when I was a graduate student at UC Berkeley,
link |
we had a professor in our department,
link |
phenomenal scientist named Steve Glickman.
link |
Steve Glickman had a colony of hyenas, spotted hyenas,
link |
that lived within caged enclosures, of course,
link |
in Tilden Park behind the UC Berkeley campus.
link |
The enclosures are actually still there.
link |
I run past there fairly often.
link |
The hyenas are no longer there.
link |
This was a federally funded field station.
link |
These animals were brought over from Africa
link |
or were bred there.
link |
And the reason why there were hyenas in Tilden Park,
link |
enclosed in Tilden Park,
link |
was because hyenas exhibit an incredible feature
link |
to their body, their hormones, and their social structure.
link |
Hyenas, unlike many species,
link |
have a situation with their genitalia
link |
where the male penis is actually smaller
link |
than the female clitoris.
link |
And I should say that the male penis itself,
link |
having seen a fair number of hyena penises,
link |
is not particularly small,
link |
which means that the hyena clitorises are extremely large.
link |
This was well-known for some time.
link |
It turns out that in these spotted hyenas,
link |
the females are dominant.
link |
So after a kill, the females will eat,
link |
then their young will eat,
link |
and then the male hyenas will eat.
link |
As well, when the female hyena gives birth,
link |
she gives birth not through the vaginal canal
link |
that we're accustomed to seeing,
link |
but through a very enlarged clitoris-like phallus,
link |
although it's not a phallus, it's a clitoris,
link |
and it literally splits open.
link |
So many fetuses die
link |
during the course of hyena development and birth.
link |
These animals have this,
link |
what could only be described
link |
as a very large sort of giant clitoris,
link |
although for a hyena, it's not giant, it's normal.
link |
And it splits open, and the baby actually comes through.
link |
The baby hyena actually comes through the tissue,
link |
and it's a very traumatic birth.
link |
A lot of tissue is torn away, et cetera.
link |
And as I mentioned, a lot of baby hyenas die.
link |
It was a mystery as to how the female hyenas have this,
link |
we'll call it masculinization,
link |
but it's really a androgen, excuse me,
link |
androgenization of the periphery of the genitalia.
link |
And it turns out through a lot of careful research
link |
done by Steve Glickman, Christine Dre, and others,
link |
that it's androstenedione,
link |
what is essentially a pro-hormone to testosterone,
link |
it's androstenedione at very high levels
link |
that's produced in female hyenas
link |
that creates this enlargement of their genitalia.
link |
So if you want to read up on androstenedione,
link |
androstenedione is made into testosterone
link |
through this enzyme, 17-beta hydroxysteroid dehydrogenase.
link |
It's a complicated pathway to pronounce.
link |
It's a fairly straightforward pathway biochemically.
link |
You may recall during the 90s and 2000s,
link |
there were a lot of performance enhancing drug scandals,
link |
in particular in major league baseball.
link |
And it was purported,
link |
although I don't know that it was ever verified,
link |
but it was purported that the major
link |
performance enhancing drug of abuse at that time,
link |
in particular players whose names we won't mention,
link |
but you can Google it if you want to find out,
link |
was androstenedione.
link |
And I actually recall long ago
link |
when you could buy androstenedione in the health food stores.
link |
And so it was sold over the counter.
link |
So a lot's changed since then,
link |
but it's interesting that these hyenas
link |
with these highly androgenized genitalia
link |
accomplish that through high levels of androstenedione
link |
Now, if that's unusual,
link |
what might be even more unusual
link |
is that a graduate student that I was working with
link |
at the time, alongside, we didn't share research.
link |
Her name was Nicola Sipka.
link |
She is actually a trained animal behavioral expert.
link |
She had trained ferrets for that show, The Beastmaster,
link |
and she would train wolves for television shows
link |
and was a dog trainer.
link |
She had these two large dogs that,
link |
unlike my dog, would actually listen to her
link |
when she would give them commands.
link |
A remarkable scientist.
link |
She was studying a species of mole
link |
that also lived in Tilden Park.
link |
People are going to start to wonder about Tilden Park.
link |
What's in Tilden Park?
link |
But this particular mole that lived there
link |
had testes for part of the year
link |
and had the capacity to transdifferentiate its testes
link |
into ovaries in order to balance out the ratio
link |
of males and females in the population
link |
to keep reproduction at appropriate levels
link |
for that certain population.
link |
So some animals are actually able to adjust
link |
whether or not they have androgenized or estrogenized gonads
link |
in order to adjust the ratios of offspring
link |
or the males and females in there for promote offspring.
link |
And the last little anecdote about this,
link |
which is also published in the scientific literature,
link |
which is weird, but I do find interesting.
link |
Hormones are so fascinating.
link |
They're just incredible to me,
link |
is going back to the marijuana plant.
link |
The marijuana plant has these estrogenic properties.
link |
And I asked a plant biologist whether or not
link |
And I asked, because there's all this stuff out there
link |
about, oh, soy does this,
link |
and these plants are highly estrogenic, et cetera,
link |
although we should probably point out
link |
that a lot of factory meats are also estrogenic.
link |
So this isn't a meat versus plants thing.
link |
But this plant biologist told me,
link |
oh yeah, there are plants that make
link |
what is essentially the equivalent of testosterone,
link |
like pine pollen, it looks a lot like testosterone.
link |
And there are other plants that make
link |
what is essentially estrogen.
link |
And I said, well, why would they do that?
link |
And plants, at least as far as I know,
link |
don't have a consciousness.
link |
They don't have a brain.
link |
They don't have neurons even.
link |
But his answer was fascinating.
link |
He said that one of the reasons
link |
why some plants have evolved this capacity
link |
to increase estrogen levels in animals that smoke,
link |
not smoke it, but then animals that consume them,
link |
I'm guessing that animals aren't smoking marijuana,
link |
although, I don't know, send me the paper
link |
if you've heard of this,
link |
is that plants have figured out ways,
link |
they've adapted ways to push back on populations
link |
of rodents and other species of animals that eat them.
link |
So plants are engaged in a kind of plant to animal warfare
link |
where they increase the estrogen
link |
of the males in that population to lower the sperm counts
link |
to keep those populations clamped at certain levels
link |
so that those plants can continue to flourish
link |
even if those animals are reproducing very robustly.
link |
And I find this just fascinating.
link |
And hormones, therefore,
link |
aren't just impacting tissue growth and development
link |
within the individual and between the mother.
link |
Remember, the placenta is an endocrine organ
link |
and the offspring.
link |
But plants and animals are in this communication.
link |
And today we're in this communication.
link |
I'm telling you that there are certain herbicides
link |
that humans are using for which there's very good data
link |
are disrupting the endocrine pathways.
link |
And so it's fascinating that humans and other animals
link |
were always in this interplay with plants
link |
and the other things in our environment.
link |
And hormones and adjusting the hormone levels
link |
of animals and plants is one way in which the environment
link |
kind of pushes back or pushes forward, if you will,
link |
in terms of promoting their wellbeing and longevity
link |
as well as you trying to promote
link |
your wellbeing and longevity.
link |
If anyone wants to see the incredible paper
link |
by Steve Glickman and colleagues,
link |
it was published in the Prosthenes of the National Academy
link |
That's Glickman et al.
link |
That was the hypothesis that it was androstenedione.
link |
And then if you just Google Glickman Hyenas Science Magazine,
link |
there's a beautiful cover article
link |
and feature all about that important discovery.
link |
It's a fascinating one.
link |
And I should mention also that those discoveries,
link |
both the moles and the hyenas weren't just impactful
link |
for the world of animal behavior and endocrinology.
link |
They've also strongly impacted understanding
link |
of conditions that show up in the clinic,
link |
which we haven't talked about today,
link |
which is actually pseudo hermaphroditism.
link |
Occasionally babies will be born where it is unclear
link |
if they are boys or girls based on the genitalia.
link |
And this has a very important ethical and other issues.
link |
Do you raise them as a boy or a girl?
link |
It's not super uncommon for this to happen.
link |
And there've been terrible cases where people have gone
link |
against the chromosomal sex and the person was very unhappy
link |
with the choice that their parents had made for them.
link |
There were also cases where they've gone
link |
with the chromosomal sex and the person was very happy
link |
about the outcome.
link |
There've been cases where they've been treated
link |
with hormones and there've been cases
link |
where they have not been treated with hormones.
link |
It's a complicated literature and it has to be sorted out
link |
on kind of a case by case basis,
link |
but it is something that does happen.
link |
And the studies on androstenedione and hyenas
link |
and in these very interesting moles,
link |
pseudo hermaphroditic moles that live in Tilden Park
link |
have impacted not just the science,
link |
but the therapeutics around those important issues.
link |
So now last but not least,
link |
I want to discuss the effects of hormones
link |
while you and I were separately in utero
link |
and the effects that that had on who we are,
link |
who we select as mates, so mate choice, sexual preference,
link |
and all other aspects
link |
of what you would call sexual development.
link |
Now, this is something that's gotten a lot of popular press
link |
and it has to do with how exposure to androgens
link |
in particular while we were in utero impacted
link |
whether or not people report as homosexual, heterosexual,
link |
identify as male or female.
link |
I'm very familiar with this work
link |
because I was a graduate student in the department
link |
that first published this work
link |
and I'm an author on the paper.
link |
I was not the main driver of the work,
link |
but I was involved in the work
link |
and I certainly know the people that did this work.
link |
First, it starts with a story.
link |
There was a researcher who's still going now.
link |
His name is Dennis McFadden.
link |
I believe he was at UT Austin back then
link |
and he was studying the auditory system
link |
and people would come into his clinic
link |
and he would, or his laboratory,
link |
and he would look at hearing
link |
and he would explore different aspects
link |
of what they call the psychophysics of hearing
link |
and understanding hearing thresholds
link |
and frequency thresholds.
link |
And he made several observations
link |
and those observations were that young males
link |
tended to have what are called autoacoustic emissions
link |
more often than young females did.
link |
Autoacoustic emissions, as the name suggests,
link |
are the ears actually making sounds.
link |
Now, these sounds have to be picked up
link |
by a special apparatus
link |
because they can hear into that frequency,
link |
but it turns out that your ears
link |
don't just take sound waves
link |
and convert them into these things,
link |
this thing we call hearing,
link |
but they also, in some cases, make sounds.
link |
So your ears are making sounds, strange, right?
link |
So it turns out that there's a sex difference
link |
in autoacoustic emissions.
link |
Turns out also that people that self-report as lesbians,
link |
they also have autoacoustic emissions
link |
significantly more than females
link |
that don't self-report as lesbian.
link |
And Dennis noticed this and published this,
link |
and it was an important discovery
link |
because it was one of the first discoveries
link |
that pointed to the fact that there are sex differences
link |
in biology that are independent of sex.
link |
I mean, this is hearing in autoacoustic emissions.
link |
And just to really illustrate what the former problem was
link |
and why this study was so important,
link |
a lot of people had explored, for instance,
link |
whether or not homosexuals had lower testosterone,
link |
for instance, in males.
link |
And actually the result often was the opposite,
link |
that gay men or men that self-report as gay
link |
often had much higher testosterone.
link |
And those studies then became controversial
link |
because people said, well,
link |
sexual behavior can relate to testosterone, et cetera.
link |
And so it became very controversial.
link |
And then there were some studies
link |
that attempted to look at the equivalent phenomenon
link |
in people that self-report as lesbian
link |
or self-report as heterosexual.
link |
And so it became very complicated,
link |
but this was an identification of a phenomenon,
link |
autoacoustic emissions, that was independent of anything
link |
that had to do with sexual or even social behavior.
link |
1998 rolls around,
link |
and I'm a graduate student at UC Berkeley
link |
and a guy by the name of Mark Breedlove,
link |
kind of an ironic name given that he worked
link |
and still works on sexual dimorphism in the brain
link |
and in the spinal cord and nervous system.
link |
And Mark, who's a phenomenal scientist,
link |
comes running down the hall, I'll never forget this,
link |
and he said, give me your hands.
link |
I was like, give me your hands.
link |
And he pulls out a ruler and he starts measuring my fingers.
link |
And he takes down a couple of measurements
link |
and then he goes away.
link |
And I'm like, what was that?
link |
Well, I was in a course that Mark was teaching
link |
And soon after we did a study that Mark directed,
link |
exploring the finger length ratios,
link |
and I'll explain what those are,
link |
of males and females
link |
and people that self-reported
link |
as homosexual or heterosexual.
link |
So let's just get to the basic,
link |
what we'll call sex differences first.
link |
These are averages I want to point out.
link |
Anytime you get into this kind of topic,
link |
people assume it's causal, but it's not causal.
link |
These are averages that I'm about to report.
link |
It is the case that the ratio
link |
of what's called the D2 to D4 digits.
link |
So the D2 is your index finger.
link |
So your thumb is D1,
link |
then D2 would be your index finger that you would point with.
link |
Middle finger is D3, which you whatever with.
link |
And then D4 is the so-called ring finger, okay?
link |
And D5 is the pinky.
link |
It is the case that the D2 to D4 ratio
link |
is greater in self-reported females than it is in males.
link |
What does that mean?
link |
It means that digit D2 and D4 are more similar in length
link |
in females than in males.
link |
And the effect is particularly, excuse me,
link |
pronounced on the right hand, although not always, okay?
link |
And it does not have to do with handedness.
link |
This D2 to D4 difference has to be measured correctly.
link |
You can't just look at somebody's hands and say,
link |
oh, their ring finger and index finger are very similar
link |
and therefore they are female
link |
or they were exposed to very little testosterone in utero.
link |
You can't look at somebody
link |
and see that their index finger is much shorter
link |
than their ring finger and say,
link |
oh, they must've been exposed to a lot of androgen.
link |
You have to actually measure it
link |
and you have to measure it correctly.
link |
You have to measure it from the base of the finger
link |
where there's that first crease all the way to the tip
link |
past the, you can't include the fingernails
link |
if you're growing fingernails,
link |
it would be logical here, folks.
link |
So you can't normally see it from the back of the hand,
link |
although I don't know if this will show up here,
link |
but if you look at the back of the hand,
link |
sometimes you can see it.
link |
In my case, for instance, let me see if I can do this.
link |
So my D4 is a little bit longer than my D2.
link |
In some people it's more pronounced
link |
and that's on my right hand.
link |
On the other hand,
link |
the difference actually is far less pronounced.
link |
It's a little bit pronounced there, but not so much.
link |
So that's sort of the typical ratio that you would see.
link |
Turns out that in mice and in humans,
link |
the more androgen that you were exposed to in utero,
link |
the smaller the D4, D2 ratio,
link |
meaning that the ring finger tends to be slightly longer
link |
than the pointer finger.
link |
because they're exposed to less androgen in utero typically,
link |
then those fingers tend to be more equal in length.
link |
And these are subtle differences and these are averages.
link |
I invite you to look up the paper.
link |
This was published in Nature in 2000
link |
and it's been replicated six times.
link |
Now here's where it gets even more interesting
link |
and potentially precarious.
link |
So we're going to step cautiously here.
link |
If you look at the finger length ratios
link |
of men that self-report as homosexual,
link |
they have either the typical male pattern
link |
or a hyper masculinized D4 to D2 ratio.
link |
Now this can't be something that's established
link |
or modified by behavior.
link |
This has to be something that was established in utero.
link |
And in fact, it's present at birth, okay?
link |
So it completely divorces the interactions
link |
between hormones and behavior.
link |
And that's an important theme that we've been talking about
link |
and we're going to talk about even more next episode
link |
is that hormones impact behavior
link |
but behavior also impact hormones.
link |
But this is a case of hormones impacting
link |
what really should be considered
link |
a primary sexual characteristic
link |
because it doesn't show up in puberty.
link |
It shows up before puberty.
link |
It's actually established in utero.
link |
And in people that self-reported lesbians,
link |
and I remember going out there and collecting these data
link |
with the collaborators on this work.
link |
Again, I wasn't the main driver on the work
link |
but I participated in some of the analysis.
link |
People that self-report as lesbians
link |
also tend to have a smaller D2 to D4 ratio.
link |
So this is consistent with the autocoustic emissions study
link |
that Dennis McFadden had published.
link |
And it points to the fact that early exposure to androgens
link |
may have an impact,
link |
not just on androgenization of the body plan
link |
but also separately on sexual preference.
link |
Now, this raises all sorts of interesting questions
link |
about biological basis of sexual preference.
link |
I'll tell you about another study,
link |
a guy named Simon LeVay who was at UCLA
link |
who trained under Hubel and Wiesel.
link |
If any of you remember early episodes on plasticity,
link |
David Hubel and Torrance and Wiesel,
link |
my scientific great-grandparents won the Nobel Prize
link |
for discovery of critical periods for brain plasticity.
link |
They defined some of the most important aspects
link |
of how we see and brain plasticity.
link |
Simon LeVay trained with them.
link |
And then Simon went on to discover
link |
that in the brains of people that self-report homosexual,
link |
there is a brain difference.
link |
And the brain difference is in an area
link |
called the interstitial nucleus
link |
of the anterior hypothalamus.
link |
And so there are published reports
link |
that was published in Science.
link |
The other work I refer to as published in Nature
link |
and then replicated no fewer than six times
link |
and the McFadden results that point
link |
to strong biological correlates of mate choice
link |
of sexual preference.
link |
And these tie directly to things like androgenization
link |
or estrogenization, meaning we could call it maleness
link |
or femaleness, but that's sort of tricky territory
link |
because of the way that we described the huge range
link |
in which sex can be defined earlier.
link |
So if you want to measure D2, D4 ratio, you're welcome to,
link |
but you also have to understand
link |
that it's not predictive of anything, right?
link |
It's just a window into the possible androgen exposure
link |
that you had early in life.
link |
There are plenty of men who report themselves
link |
as heterosexual who are out there
link |
who have similar or have D2, D4 ratios to females.
link |
And there are plenty of females whose index fingers
link |
are shorter than their ring fingers
link |
and they're perfectly happy
link |
or they say they're perfectly happy
link |
and we are inclined to believe them being heterosexual.
link |
So there's variation.
link |
In fact, Mark tells a really good joke.
link |
If you want to know whether or not somebody is homosexual
link |
or heterosexual, simply look at their hands,
link |
look at their D2, D4 ratio and guess heterosexual
link |
and you'll be right 96% of the time
link |
because 96% of the time people report themselves
link |
as heterosexual on average, those numbers might be changing.
link |
So the joke really is a joke on science
link |
because that falls within the realm
link |
of statistical significance
link |
and yet it really illustrates the fact
link |
that none of this is causal,
link |
but it's nonetheless very interesting
link |
because it means that hormones are organizing
link |
the brain early in development
link |
in ways that can potentially impact same
link |
or opposite sex partner choice later in life.
link |
Now, of course, there are other things
link |
that can impact opposite sex
link |
or same sex partner choice later in life.
link |
The study did not look at people who reported bisexual.
link |
There hasn't been a lot of studies on that yet.
link |
One thing that's very interesting
link |
for which there are some good scientific data
link |
but there's also some controversy
link |
is that it appears that the probability
link |
of a male human self-reporting as homosexual
link |
increases with the number of older brothers that he has.
link |
Now, that doesn't mean if you have an older brother
link |
even if you have 10 older brothers
link |
that you are sure to self-report as homosexual,
link |
but statistically it becomes more likely
link |
that somebody will with each successive older brother
link |
And the idea that's starting to emerge
link |
in the developmental neuroendocrinology landscape
link |
is that there's a record within the mother
link |
of how many male fetuses she's carried
link |
because male fetuses are secreting certain things,
link |
dihydrotestosterone, other things
link |
that can feed back onto the genome.
link |
So these could be epigenomic effects
link |
or onto the placenta itself
link |
so that there's a higher probability
link |
in subsequent pregnancies
link |
that offspring will self-report as homosexual.
link |
So it's a fascinating area of biology.
link |
And as you've noticed today,
link |
none of this deals with the current controversies
link |
around gender and how many genders and sex, et cetera.
link |
That's a separate conversation that is by definition
link |
grounded in the kind of concepts
link |
we've been talking about today
link |
and needs to take place taking into consideration
link |
all of the aspects of sex and the effects of hormones
link |
both on the body, on the brain.
link |
We didn't talk a lot about spinal cord
link |
but we will in the next episode
link |
but we can just say on the brain and the periphery
link |
early effects, late effects, acute effects
link |
meaning effects that are very fast
link |
of levels of hormones going up or down
link |
something that absolutely happens
link |
during and across the menstrual cycle
link |
as well as long-term effects
link |
like the effects of these hormones on gene expression.
link |
So today, as always, we weren't able to cover
link |
all things related to sex and hormones
link |
and sexual differentiation or development.
link |
There's no way we could
link |
but we have covered a lot of material.
link |
We talked about some effects of environmental toxins.
link |
We talked about potential effects of cell phone radiation
link |
something I never thought that I would be talking about
link |
especially not in a podcast
link |
but for which there are interesting emerging data.
link |
We talked about considerations about evening primrose oil
link |
and its estrogenic effects, about creatine
link |
and its pro DHT effects, about cannabis alcohol
link |
about plants exerting warfare on animals
link |
by increasing aromatase
link |
the conversion of testosterone to estrogen.
link |
We talked about hyenas with giant clitorises
link |
and we talked about moles that can convert
link |
from having ovaries to testicles.
link |
And throughout this Costello has been snoring nonstop.
link |
He missed all of it
link |
although he might be learning it in his sleep
link |
And I do understand it's a lot of information
link |
a lot of detail as always, I just want to remind you
link |
you don't have to absorb all the information at once.
link |
Next episode, we are going to be talking about
link |
the science of sex, the verb, actual reproduction.
link |
We're also going to be talking about effects of hormones
link |
on various aspects of behavior
link |
and ways to modulate hormones
link |
through the use of behavior, supplementation.
link |
Also, we'll touch on diet and nutrition a bit.
link |
And we're going to talk about interactions
link |
between those things and behavior
link |
as they relate to important themes
link |
like sex and reproduction, like workplace performance
link |
like motivation and drive, and even anxiety.
link |
There's a very interesting relationship
link |
between hormones and anxiety
link |
and the desire to explore novelty.
link |
So just remember as we go forward
link |
that hormones affect behavior
link |
and behavior affects hormones
link |
but that doesn't mean that cutting off your index finger
link |
will increase your testosterone.
link |
Many of you have asked how you can help support the podcast
link |
and we thank you for the question.
link |
There are several ways to do that.
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The first one is to subscribe on YouTube.
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If you haven't subscribed to the YouTube channel already
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As well, please hit the subscribe button
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We do release episodes every Monday
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but we also occasionally release short clips in between.
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As well, if you could subscribe on Apple and or Spotify
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And on Apple, you have the opportunity to leave us
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On YouTube, please do leave us comments and suggestions
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Also ask us any questions you have about the material.
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Also, if you could tell people about the podcast
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As well, if you're interested in supplements
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A lot of supplement brands out there
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They partnered with important and stringent institutions
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So that's why we partnered with Thorne.
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If you want to try any of Thorne's products
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So once again, I want to thank you
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and today neuroendocrinology with me.
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And as always, thank you for your interest in science.
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I'll see you next time.