In this episode, I discuss how hormones such as testosterone and
estrogen and their derivatives impact the early development of the
brain and body and their maturation. I review published data on
environmental factors shown to powerfully alter hormone pathways in
animals and humans and the effects of cannabis, alcohol and cell
phones on testes, sperm, ovaries and hormones. I describe the
predictable relationship between genes, beard growth and balding
patterns, and the importance of estrogen for brain development in
people of all chromosomal sexes. Finally, I discuss how the hormones
we are exposed to in the womb shape the relative length of our finger
digits, the sounds our ears make (yes you read that correctly), and
how those correlate with people's self-reports of their sexual
preferences. As always, basic information and tools are discussed.
- Introduction
- Announcement: Mood Meter App Works Again
- Maximizing Learning from the Podcast
- New Non-Sleep Deep Rest Protocol, Spanish Subtitles
- Sexual Differentiation: Hormones, Neurons & Behavior
- Hormones Basics
- Sperm Meets Egg, Chromosomal Sex, Gonadal Sex
- Y Chromosome Inhibition of Feminization
- Placenta Is An Endocrine (Hormone-Producing) Organ, Adrenal Testosterone
- Hormonal Sex, Morphological Sex
- Hormones Fast & Slow, Sex Steroids Can Turn On Genes
- Masculinization, Feminization, Demasculinization, Defeminization
- Primary Sexual Characteristics: DHT Drives Penis Development
- Secondary Sexual Characteristics
- Penis Sprouting: Guevedoces
- Estrogen, NOT Testosterone, Masculinizes The Brain
- Breast Development In Males: Aromatase; Puberty, & Steroids in Athletes
- Estrogen Powerfully Controls Brain Development In All Individuals
- Avoiding Hormonal Disruption In Children & Adults: Specific Oils, Creams, Etc.
- Environmental Endocrine Disruptors, Sperm Count Decline, Vincloziline
- Androgen Insensitivity Syndrome: Hormones Need Receptors, SARMS
- Estrogen Establishes “Masculine” Brain Circuits, Testosterone
- Cannabis, Alcohol: In Babies, Puberty & Adults
- Cell Phone Technology: Effects On Hormones, Ovaries, & Testicles
- Beards & Baldness Patterns Around the World, DHT, 5-alpha-reductase
- Creatine & DHT/Hair Loss
- Predicting Aging Rates By Pubertal Rates
- Hyenas, Baseball, & Hypertrophied Clitorises: Androstenedione
- Intersex Moles
- Marijuana Plants, Pollens: Plant-To-Animal “Warfare”
- Finger Length Ratios, Prenatal Hormone Exposure & Sexual Orientation
- Brain Dimorphisms with Sexual Orientation
- “Older Brother Effects”: Male Fetuses Might Change Mothers & Subsequent Brothers
- The Path Forward & A Warning
- Support & Your Questions
- HubermanLab #Testosterone #Estrogene
[upbeat music] - [Andrew Huberman] Welcome to The Huberman Lab
Podcast, where we discuss science and science-based tools for everyday
life. -- I'm Andrew Huberman and I'm a professor of Neurobiology and
Ophthalmology at Stanford School of Medicine. This podcast is separate
from my teaching and research roles at Stanford. It is however part of
my desire and effort, to bring zero cost to consumer information about
science and science related tools. In keeping with that theme, I'd
like to thank the sponsors of today's podcast. Our first sponsor is
Inside Tracker. Inside Tracker is a personalized nutrition platform
that analyzes data from your blood and DNA to help you better
understand your body and help you reach your health goals. I'm a big
believer in blood tests and DNA tests for the simple reason that many
of the factors that are important for your short-term and long-term
health and overall wellbeing can only be analyzed from blood and DNA
tests. Things like metabolic factors and hormone levels, really can
only be assessed accurately from blood and DNA. The thing I like about
Inside Tracker is you don't just get back levels of different hormones
and metabolic factors and so forth, you also get directives. It has a
dashboard that's very easy to use that tells you based on your data,
what sorts of foods you might want to eat more of or less of. What
forms of exercise you might want to do more of or less of. It's really
a wonderful way to assess how your behaviors and lifestyle choices are
interacting with what's going on deep within your biology. Inside
Tracker makes all of that super easy to understand. It's also really
easy to get the blood tests and DNA tests taken. You can go to a local
location or they can send somebody to your home if you prefer that. If
you'd like to try Inside Tracker you can visit
insidetracker.com/huberman to get 25% off any of Inside Trackers
plans. Use the code Huberman at checkout. That's
insidetracker.com/huberman to get 25% off any off any of Inside
Tracker's plans and use the code Huberman at checkout. Today's episode
is also brought to you by Helix Sleep. Helix Sleep makes mattresses
and pillows that are designed to meet your sleep needs, in order to
optimize your sleep. I've done several episodes of this podcast and
there's a ton of information out there pointing to the fact that
getting really deep restful sleep each night is vital for mental and
physical health. And the mattress that you sleep on and the pillow
that you use is very important for getting optimal sleep. Helix Sleep
has a brief two minute quiz that you can take. It asks you questions
like, "Do you sleep on your side, or your back or your stomach or
maybe you don't know? Do you tend to run hot or cold as you sleep or
maybe you don't know?" That two minute quiz matches you to a mattress
and pillow that's ideal for your sleep needs. I took this quiz, I
matched to the mattress they call "The Dusk," D-U-S-K. And I've been
sleeping on "The Dusk" mattress for many months now and I've been
sleeping better than I ever have before. It's really wonderful to have
a really good night's sleep on a consistent basis. It's a total game
changer. So if you're interested in upgrading your mattress, you can
go to helixsleep.com/huberman. Take their two minutes sleep quiz and
they'll match you to a customized mattress. And you'll get up to $200
off any of their mattress orders and two free pillows. So that's
helixsleep.com/huberman. Take the two minutes sleep quiz they'll match
you to a mattress. And if you order one of their mattresses, you'll
get up to $200 off any of their mattresses and two free pillows. They
have a 10 year warranty and you get to try out the mattress for 100
nights risk-free and if you don't like it they'll pick it up and take
it away. If you love it, then you keep it. And I think there's a very
good chance that you're going to love it, I certainly loved mine. And
today's episode is also brought to you by Athletic Greens. Athletic
Greens is an all-in-one vitamin mineral probiotic drink. I started
using Athletic Greens way back in 2012. And so I'm delighted that
they're sponsoring the podcast. I started using Athletic Greens
because I found it rather confusing to figure out what vitamins and
minerals to take. And in Athletic Greens, I get all the vitamins and
minerals I need to cover my bases. As well probiotics are really
important. Probiotics have been shown now in numerous studies to be
important for the gut microbiome, which impacts the gut brain axis, as
well as various aspects of bodily health. So in Athletic Greens I get
vitamins, minerals and probiotics. I also really like the way it
tastes. It's a greens drink, so you mix it with some water. You could
mix it with something else like juice if you like. I mix mine with
water and lemon juice and I drink it once or twice a day. If you want
to try Athletic Greens you can go to athleticgreens.com/huberman. And
if you do that, you'll claim their special offer, which is to get a
years supply of vitamin D3 K2. There's now also a wealth of data
showing that Vitamin D3 is important for various aspects of brain and
body health. So that's athleticgreens.com/huberman for Athletic Greens
and a years supply of Vitamin D3 K2. You'll also get five free travel
packets. The travel packets are just a really convenient way to take
Athletic Greens when you're on the road, in the car or on a plane or
just moving around. You just empty one of the packets into a water
bottle or a glass and mix it up really quickly. It saves any kind of
mess or anything of that sort. So once again
athleticgreens.com/huberman to get Vitamin D3 K2. That's a year supply
and the five free travel packs. It's a new month, which means it's a
new topic here at the Huberman Lab Podcast. For the next four or so
episodes, we're going to be talking all about hormone affects on the
brain and body. So that's a huge number of different topics. We're
going to talk about sex. We're going to talk about reproduction. We're
going to talk about puberty a little bit more. We talked about that in
a previous episode. We're going to talk about menopause. We're going
to talk about birth control. We are going to talk about aggression,
competition, winning, losing. Basically, we're going to cover as much
about hormones as we possibly can in this month and in doing so we are
going to go deep into tools and protocols. We are also going to talk
about a lot of tools that relate to things that you might not want to
do in order to optimize hormone health, regardless of stage of life or
your goals et cetera. So it's sure to be a month rich with discussion,
rich with tools and you're going to learn a lot of neuroscience and
endocrinology. There's actually a field of neuro-endocrinology. It's
actually where I started my graduate work. I did a masters in it.
Which has only to say that I love the topic. I have a lot of friends
that work on this topic, many of whom I've consulted for these
episodes. And I'm really excited to share the information with you.
Before we dive into today's episode, "All About Emotions and Sex." I
want to just to have a few announcements that are designed to point
you to some useful resources.
Last episode, "Talking About The Science of Emotions and
Relationships." I mentioned the Mood Meter app. The Mood Meter App was
developed by people out at Yale University who study the biology and
psychology of emotions. It's a really wonderful app. However, many of
you quickly told me that the Mood Meter App isn't available in your
area. You went to the link we posted and it just was saying not
available in your area. The situation was actually a lot worse than
that. The situation was that, when we recorded the episode the Mood
Meter App was working. I know 'cause I downloaded a fresh copy of it
to my phone. And then in the ensuing weekend, they took the Mood Meter
App down for some repairs. The Mood Meter app is now up. It is
available. I want to be really clear. It's not an app I'm affiliated
with. I'm just mentioning it to you. They don't know me. I know them,
but they don't know me. So we don't have any kind of business
relationship. They do charge 99 cents for the app. I think the free
version has disappeared in the last year or so. So that's Mood Meter
app. We'll provide the link again and the link should be working.
Hopefully they won't take it down again, in between this announcement
and the release of this episode. Also just want to take a step back
for a moment and talk a little bit about the logic of how to make the
most of the information on the Huberman Lab Podcast.
I tend to throw out a lot of information about a given topic. Many of
you have pointed out however, that I don't cover certain things. And
once again I'll just say the goal is always to be accurate, but
there's no way I can be exhaustive. There's no way I can cover
everything for a particular topic. The good news is we have time. My
goal, at least in the first year of the Huberman Lab Podcast, is to
give you a basis, a foundation in these different topics of neuro-
plasticity, focus, sleep, hormones et cetera. And of course, to
provide tools along the way. We are going to host guests, I've
actually started recording with some of these guests already. And even
those episodes will include a little what we call primer. A little
description of the basics of a given topic so that you can get more
information from those topics. My goal really is to educate you in
these topics, give you a foundation in these topics and allow you to
start exploring them here in the episodes with our future guests, but
also in other podcasts and books and other sources of information. So
for those of you that are saying, "It's too much information." I just
encourage you to remind yourself that you have a pause button you can
return to it. Everything's timestamped. For those of you that feel,
it's not enough information I'm not covering enough. Just know that
this is just the beginning. We didn't intend to do this for a very
long time and we will be thorough over time. So thanks for your
patience and please be patient with yourselves. There's no reason why
you have to digest all the information in one swoop. The other thing
is that I've been told both that I speak too fast and speak too slow.
So there's a wonderful solution to this. If I speak too fast or too
slow you can adjust the speed in YouTube. If you're listening in a
different format, I think you also can adjust the speed of playback.
So that's something that wouldn't be possible in the classroom, but
you may find useful. And then last but not least, I want to point
people again to this NSDR, non-sleep deep rest protocol, that the
folks over at Madefor have put out as a free resource.
It does, as many of you pointed out, bear resemblance to things like
yoga nidra and other forms of meditation. But what we've done is we've
stripped out intentions or any kind of the verbiage related to what
some people might perceive as kind of related to the yoga community or
specific to kind of new age-y type techniques. Not because we don't
like yoga nidra. In fact, I've done yoga nidra daily for almost the
last goodness, eight years of my life. I love yoga nidra, but
sometimes the complicated language can be a separator and can
discourage people from taking on these protocols that are extremely
useful. So NSDR is intentionally generic. It's designed to bring you
into a state of deep relaxation through a combination of breathing and
body scan. There's the you too script over at Madefor which is linked
in the caption. And many people find that they prefer that to scripts
like yoga nidra. Scripts where they're doing intentions and they're
hearing a lot of kind of unusual language around the process. This is
just very basic and I hope you'll enjoy it. And if you prefer the more
typical yoga nidra scripts then go with those. There are many of them
available on the internet and elsewhere. And last but not least I want
to point out that, all our episodes now are subtitled both in English
and in Spanish. So for those of you that prefer to digest this
information in Spanish, that's now available to you in the subtitles.
Today we're going to talk about The Science of Sex.
In particular, sexual differentiation. Now that's a complicated topic
because sex is both a adjective, a noun and a verb, depending on the
context. Today we're going to talk about the hormonal effects and the
neural effects of particular events that happen during development and
how those guide adolescent and adult behavior, including sexual
preference. It's an area that's fascinating and for which, there are
actually very solid textbook findings. So textbook findings means,
that there are many studies that have been aggregated over decades.
That point to what we now know to be absolute truths in terms of how
hormones affect brain development, how the brain impacts hormonal
development and how those interact to control behavior for instance.
We are also going to talk about reproduction, the verb sex. And of
course, sex the verb, can also be carried out independent of
reproduction. It's not always, in particular in humans, just to
produce offspring. So that's going to be covered in the next episode,
but you absolutely need to understand the information in this episode,
in order to make sense of the information in the next episode. So,
today we're going to explore hormones. What they are, how they work,
what leads to masculinization or feminization of the brain and body?
I'll just throw out one really interesting fact that perhaps most of
you didn't realize that hormones have direct effects on the body. Most
people know that because there are hormone differences and sex
differences in bodies in terms of genitalia and body hair,
distribution of body hair et cetera. But there are also effects of
hormones on the brain directly and believe it or not there're also
effects on the spinal cord. On the neurons and structures within the
spinal cord that impact in a very direct way, what sorts of behaviors
are possible. So it's a fascinating area, you might notice I'm going
to go a little bit more slowly through this topic than I normally do.
I want to be extremely careful with my language. Some of these topics,
some of you may be thinking are extremely sensitive, right? And of
course, any discussion about sex and reproduction is a sensitive one.
But today we're just talking about the biology. We're not getting into
the cultural constraints or the cultural dialogue. What we're trying
to do today is really get to the biology, the physiology, the
endocrinology and the behavior. So let's start by talking about what
hormones are just to remind you and what they do.
Hormones by definition, are a substance, a chemical that's released in
one area of the body. Typically from something we call a gland,
although they can also be released from neurons. But they're released
often from glands, that travel and have effects both on that gland but
also on other organs and tissues in the body. And that differentiates
hormones from things like neurotransmitters, which tend to act more
locally. So that's important. A hormone is a substance secreted at one
location in the body, travels, and has impact on things elsewhere in
the body. Examples of tissues that produce hormones would be the
thyroid, the testes, the ovaries et cetera. And then of course there
are areas of the brain like the hypothalamus and the pituitary, which
are closely related to one another and release hormones that cause the
release of yet other hormones out in the body. So we're going to cover
all this. If you don't know anything about endocrinology, you're still
going to be able to understand today's discussion. And we're going to
start with a discussion about, what hormones actually do, to create
this thing that we call masculinization or feminization.
So let's start with development. Sperm meets egg. Everything that
happens before that is a topic of the next episode. But, sperm meets
egg. This is mammalian reproduction. And that egg starts to duplicate,
it starts to make more of itself. It makes more cells. And eventually
some of those cells become skin. Some of those cells become brain.
Some of those cells become muscle. Some of those cells become fingers.
All the stuff that makes up the brain and body plan. In addition,
there are hormones that come both from the mother and from the
developing baby, the developing fetus. That impact. whether or not the
brain will be what they call organized masculine or organized
feminine. And as I say this, I want you to try and discard with the
cultural connotations or your psychological connotations, of what
masculinization and feminization are. Because we're only centering on
the biology. So typically, people have either two X chromosomes, and
the traditional language around that is that person is female, right?
Or an X chromosome and a Y chromosome and that person will become
male. Now it's not always the case. There are cases where it's XXY,
where there two X chromosomes plus a Y chromosome. There are also
cases where it's XYY. Where they're two Y chromosomes. and these have
important biological and psychological impacts. So the first thing we
need to establish is that there is something called chromosomal sex.
Whether or not they're two X chromosomes, or an X and Y chromosome, is
what we call chromosomal sex. But the next stage of separating out the
sexes, is what we call gonadal sex. Typically not always, but
typically if somebody has testes for their gonads, we think of them as
male. And if somebody has ovaries, we think of them as female.
Although that's not always the case either. But let's just explore the
transition from chromosomal sex to gonadal sex, because it's a
fascinating one that we all went through in some form or another. So
this XY that we typically think of as promoting masculinization of the
fetus. We say that because on the Y chromosome there are genes and
those genes have particular functions that suppress female
reproductive organs.
So on the Y chromosome there's a gene, which encodes for something
called Mullerian Inhibiting Hormone. So there's actually a hormone
that's programmed by the Y chromosome that inhibits the formation of
Mullerian Ducts, which are an important part of the female
reproductive apparatus. That's critical because, already we're seeing
the transition between chromosome Y chromosome and gonad. And other
genes on the Y chromosome promote the formation of testes. So there
are genes like the SRY gene and other genes that promote the formation
of testes, while they also inhibit the formation of the Mullerian
Ducts. So the transition from chromosomal sex to gonadal sex is a very
important distinction. It's kind of a fork in the road that happens
very early in development while fetuses are still in the embryo. Now
what's interesting as well, is that just because there's a Y
chromosome that can suppress Mullerian Duct formation and there are
other genes on the Y chromosome that promote testes development.
The placenta itself is an endocrine organ. I think most people don't
know this but the placenta is an endocrine organ as well. The mother,
which of course is carrying the fetus has an adrenal gland which can
produce testosterone. There are instances for example, where a mother
has either a tumor or for some other reason is secreting large levels
of testosterone while carrying a fetus that is XX. And that leads to
what we would call masculinization of certain aspects of the fetus.
Typically, that will be enlarged clitoris. There also some examples of
other phenotypes on the body that are created even though it's a
purely XX chromosomal baby. So we have to distinguish between
chromosomal sex, gonadal sex.
And then there's what we call hormonal sex. Which is the effects of
the steroid hormones, estrogen and testosterone and their derivatives,
on what we call morphological sex or the shape of the baby and the
human and the genitalia and the jaw and all these other things. And so
it actually is quite complicated. So you know, it's a long distance
from chromosomes to gender identity and gender identity has a lot of
social influences and roles. This is an area that right now is very
dynamic and in the discussion out there as you know. But just getting
from chromosomal sex to what we would call gonadal sex and hormonal
sex and morphological sex, involves a number of steps. So today we're
going to talk about those steps. And there's some fascinating things
that do indeed relate to tools. Do indeed relate to some important
behavioral choices. Important choices about things to avoid while
pregnant. And for those of you that are not pregnant, things to avoid
if you're thinking about eventually having children. And that is not
to drive development in one direction or another, but there are
examples where there are some deleterious things in our environment
that can actually negatively impact what we call sexual development
overall, regardless of chromosomal background. So let's get started
with that.
Let's talk a little bit more about what hormones do. Hormones
generally have two categories of effects. They can either be very fast
or they can be very slow. There are hormones like cortisol and
adrenaline, which act very fast. Adrenaline can increase your heart
rate very fast when secreted into the body. Cortisol can be a little
bit slower, but it also can have some very fast effects. And then
there are hormones like. Like testosterone and estrogen, which we
refer to as the sex steroid hormones. The sex steroid hormones can
have quick effects through signaling. Meaning they can attach to cells
and make those cells do different things. They can have a actually
quite quick effects on the brain. A lot of people don't know this, but
there are some very fast effects of estrogen and testosterone as well
as long-term effects. These molecules, for those of you that are
interested, are what it called lipophilic. Which just means that they
like fatty stuff, they can actually pass through fatty membranes. And
because the outside of cells, as well as the what's called the nuclear
envelope. Where all the DNA contents and stuff are stuffed inside, are
made of lipid, of fat. These steroid hormones can actually travel into
cells and then get into the DNA. Basically interact with the DNA of
cells in order to control gene expression. So they can change the
sorts of things that cells will become and they can change the way
that cells function in a long-term way. And that's actually how the
presence of these genes like SRY and Mullerian inhibiting hormone,
lead to reductions or elimination I should say, of things like the
Mullerian Ducts and promote instead what's called in males the
Wolffian Ducts. Or promote the development of testes rather than
ovaries. So all you need to know is that hormones have short-term and
long-term effects. And the long-term effects are actually related to
their effects on genes and how those genes are expressed or repressed,
in order to prevent them from having particular proteins made. So
these hormones, these steroid hormones are exceedingly powerful. And
if we're going to have a discussion about masculinization or
feminization et cetera, you also need to think about the counterpart.
It's not just about masculinizing the body or feminizing the body and
brain, it's also about demasculinize the brain in many cases, as a
normal biological function of typically of XX females. And de
feminization, the suppression of certain pathways that are related to
feminization of the body and brain. But there are some really
fascinating twists in this story. So I've just thrown a lot of biology
at you, but this is where it all starts to get incredibly surprising.
You would think that it's straightforward, right? You have a Y
chromosome you suppress the female reproductive pathway like the
Mullerian Ducts. You promote the development of testes and then testes
make testosterone. And then it organizes the brain male and it wants
to do male like things. And then in females you get estrogen and it
wants to do female like things. And air quotes here for all of this.
It turns out that isn't how it works at all. Here's where it's
interesting. We have to understand that there are effects of these
hormones, testosterone and estrogen. on what are called primary sexual
characteristics. Which are the ones that you're born with. Secondary
sexual characteristics, which are the ones that show up in puberty.
And these are happening in the brain and body and spinal cord. And so
I'm going to disentangle all this for you by giving you some examples.
First, let's talk about the development of primary sexual
characteristics. The ones that show up at birth. And one of the more
dramatic examples of this comes from the role of testosterone in
creating the external genitalia. Now you might think it's just
straight forward. If there's a testes, 'cause there's a Y chromosome.
You know, you've got a gene that codes for the development of testes,
you get testosterone and the penis grows and the baby is born with a
penis. You know, one of the first things that happens when the baby
comes out is they look at the genitalia, and they try and make an
assessment on whether or not it's a quote boy or it's a quote girl,
right? That's been done for a very very long time throughout human
history. It turns out that it's not testosterone that's responsible
for the development of the penis in a baby that has an X chromosome
and a Y chromosome. It's a different androgen. Androgen is just a
category of hormones that includes testosterone, but testosterone is
converted in the fetus to something called dihydrotestosterone. And
that's accomplished through an enzyme called 5-alpha-reductase. Now
dihydrotestosterone has important effects later in life too. We will
talk about those. In fact, if you just want to know,
dihydrotestosterone is what we would call the dominant androgen in
males. It's responsible for aggression. It's responsible for a lot of
muscular strength. It's involved in beard growth and male pattern
baldness. We're going to talk about all of that. But
dihydrotestosterone has powerful effects in determining the genitalia,
while the baby is still in the embryo. So this ends. There's
testosterone that's made. And that testosterone gets converted by this
enzyme 5-alpha-reductase in a little structure called the tubercle.
That tubercle will eventually become the penis. So you say, "Okay,
straight forward." This testosterone is converted to
dihydrotestosterone. And then if there's dihydrotestosterone it
controls penis growth. And indeed that's the case. So that's a primary
sexual characteristic. That baby will then grow up and later during
puberty there will be the release of a molecule. I talked about this
last episode called Kisspeptin. K-I-S-S-P-E-P-T-I-N kisspeptin, which
will cause the release of some other hormones Connatural releasing
hormone, Luteinizing hormone will stimulate the testes to make
testosterone.
So in puberty, testosterone leads to further growth and development of
the penis, as well as the accumulation of or growth of pubic hair, a
deepening of the voice, all the secondary sexual characteristics,
okay? So dihydrotestosterone creates what we would call the typical
masculine phenotype for primary sexual characteristics and produces.
Testosterone excuse me, produces secondary sexual characteristics
during puberty. There's a very interesting phenomenon that was
published in The Journal of Science in the 1970s, for which now
there's a wealth of scientific data.
And this relates to a genetic mutation, where 5-alpha-reductase the
enzyme that converts testosterone to dihydrotestosterone doesn't
exist. It's mutated in a way into a genome that it doesn't exist. And
this actually was first identified in the Dominican Republic. It has
shown up elsewhere. It's quite rare, but where it shows up it's
robust. What happens is baby is born. Typically when a baby is born
they don't measure chromosomes. They don't look at chromosomal sex XX
or XY. That's not typically done nowadays. Baby is born. If you were
to look at that baby, it would look female. There would be very little
or no external penis. And so people would say, "It's a girl." And they
might, you know, have the celebration it's a girl. And I guess now
they call them "Gender Reveal Parties" or something like that. I don't
know about this, but anyway. They would reveal. The baby would reveal
its external genitalia simply by being there and being naked when it's
born. It has nothing to do with gender, it has to do with genitalia
and sex. That baby would be born. And what was observed is that, from
time to time, that baby after being raised as a girl, perfectly happy
as a girl would around the age of 11 or 12 or 13, would suddenly start
to sprout a penis. There's actually a name for this, it's called
Guevedoces. Which the translation is more or less, penis at 12. And as
strange as this might sound, it makes sense if you understand the
underlying mutation. What happens in these children, these Guevedoces,
is that the child is born. It has testes which are not descended, so
up in the body. They're not making a lot of testosterone early on.
They weren't able to convert testosterone to dihydrotestosterone
because they lack this enzyme 5-alpha-reductase. As a consequence, the
primary sexual characteristic of external male genitalia, penis,
doesn't develop. And then what happens is the baby grows up as a young
child essentially is treated as a girl. Generally they report being
pretty comfortable as girls, although not always. And then
testosterone starts getting secreted from the testes 'cause kisspeptin
in the brain signals through gonadotropin and luteinizing hormone and
travels down to the testes, the testes start churning out testosterone
and there's a secondary growth of the penis. And all of a sudden
there's a penis. And this leads to some very complicated situations in
families and culturally. And actually the outcomes in terms of whether
or not these children decide to self identify as males or females and
how people treat them actually varies quite a lot. There's actually
been kind of an adopting of a third category of sex and gender in
these Guevedoces for in order to just offer them the opportunity to
explore not just what would be a typical kind of girl or woman or boy
or man phenotype, but something in between. Something that some people
call intersex although intersex and pseudo hermaphroditism is actually
a separate thing altogether. So it's fascinating and the point here is
that dihydrotestosterone not testosterone is responsible for this
primary growth of the penis. And that testosterone later is involved
in the secondary sexual characteristics deepening in the voice, et
cetera. Now this is where the information gets even more interesting
and applies to essentially everybody.
You might think that testosterone because it masculinizes the body in
the secondary sexual characteristic way. And because
dihydrotestosterone another androgen, masculinizes the primary sexual
characteristics. The growth of the penis early on, that testosterone
must masculinize the brain. And there are in fact aspects of
masculinization of the brain and body, that are independent of
genitalia. Now it might be obvious to some of you, but some people
probably don't realize that. Yes indeed the brain has receptors for
testosterone. It also has receptors for estrogen. But the fascinating
thing is that if you look at the brains of people that have Y
chromosomes and that have testes and that make testosterone, and you
look at the brains of people that don't have Y chromosomes or testes
and therefore make far less testosterone in general, what you realize
is that the cells in the brain that differ between what I'll call
males and females, but between XY, and XX have receptors for
testosterone, but the masculinization of the brain is not accomplished
by testosterone. I want to repeat this. The masculinization of the
brain is not accomplished by testosterone. It is accomplished by
estrogen. Testosterone can be converted into estrogen by an enzyme
called aromatase. This is vitally important to understand.
Testosterone can be converted into estrogen by something called
aromatase.
I'll give an example of where this happens later in life, to just
illustrate the principle and really embed it in your mind. During
puberty in boys, XY chromosome individuals. It's not uncommon for
there to be transient or sometimes long lasting breast bud
development. Testosterone goes up during puberty, for the reasons we
talked about before. And some of that testosterone gets converted into
estrogen by an enzyme called aromatase. Aromatase is made by several
sources in the body. One of the main sources is body fat. So it can
make a lot of aromatase. Sometimes you'll even see fairly dramatic
breast development in males during puberty. Sometimes it's transient,
sometimes it's not. The other place where you see this is in athletes
and bodybuilders that take a lot of anabolic steroids. That take high
levels of androgens. So they'll be taking testosterone at super
physiological doses. Sometimes not always. They will convert some of
that testosterone into estrogen and they'll get what's called
gynecomastia. Which is the development of male breast tissue.
Sometimes they'll get it cut out surgically. Other times they'll start
trying to take estrogen blockers in order to try and suppress it or
they'll try and block prolactin. It's a topic that we're going to get
into in more detail. But what's important here is to understand that
testosterone can be converted to estrogen by aromatase. Aromatase is
not just made in body fat. There are neurons in the brain that make
aromatase and convert testosterone into estrogen. And it is
testosterone converted into estrogen.
In other words, it's estrogen that masculinizes XY individual. That
masculinizes the brain. And this has profound effects on all sorts of
things. On behavior, on outlook in the world et cetera. But I think
most people don't realize that it's estrogen that comes from
testosterone that masculinizes the male brain, the XY brain. Not
testosterone nor dihydrotestosterone.
So I just want to mention some tools. You might be asking yourself,
"How could tools possibly come up at this stage of the conversation
where we're talking about sexual development and we're talking about
the differentiation of tissues in the body." Well, this is true both
for children and parents and adults. I want to emphasize that there
are things that are environmental and there are things that people use
in their homes sometimes that actually can impact hormone levels and
can impact sexual development in fairly profound ways. And I want to
be very clear, this is not me pulling from some rare journal have
never heard of it. This is pulling from textbooks. In particular,
today I'm guiding a lot of the conversation on work that on
"Behavioral Endocrinology," is a book by Randy Nelson and Lance
Kriegsfeld. True experts in the field. I'm going to talk about some of
the work from Tyrone Hayes from UC Berkeley about environmental toxins
and their impacts on some of these things like testosterone and
estrogen. I'm going to touch into them. I'm going to give some
anecdotal evidence that's grounded in studies, which we will provide
in the caption or that I'll reference here. One of those that's
actually really interesting but helps illustrate the principle that
we've been talking about is. A few years ago, there was a lot of
excitement about Evening Primrose Oil. Evening Primrose Oil is in a
lot of products that typically are associated with skin beauty and
skin health. And so I'm generalizing here. But typically it was
mothers or sisters that were using it. And there were actually
examples starting to crop up of young boys getting accelerated breast
bud development from skin contact with women were using Evening
Primrose Oil. So Evening Primrose Oil is chemically a lot like
estrogen and it has a lot of estrogenic compounds. There are a number
of things out there like this. So believe it or not things like pine
pollen look very much like testosterone structurally. They are more or
less are testosterone. Their bioavailability in humans isn't as clear.
Evening Primrose Oil has a lot of estrogenic elements to it. Just
structurally how it's built. And so there were cases where boys were
understandably you know, being hugged by their mom or maybe even like
showering and taking. you know using the Evening Primrose Oil
solution. Those things will actually change levels of estrogens in
boys and girls. And so this wasn't just an issue for young boys. This
is also an issue for young girls. So it's not that Evening Primrose
Oil is bad, it's just that many of you have probably heard about the
dangers of Soy Isoflavones and things like that. The impact of soy on
estrogen levels is, there are some decent evidence to support that.
However, there's a lot of other factors that are more severe. And one
of those is this Evening Primrose Oil. So regardless of age, let's
just put it this way because people might be wanting to drive their
hormones more estrogenic or more androgenic. How could I know which
what your preference is? I don't know. But in any case, things like
pre Evening Primrose Oil can actually promote estrogenic pathways in
the body and some of it can go transdermal. Likewise, because
testosterone replacement therapy is fairly widespread nowadays. And
some people accomplish that through cream. It's pretty well understood
that, if someone's taking that they want to avoid contact with anyone.
Skin contact with anyone that is trying to promote more estrogenic
activity in their body. And especially in children. So that's one. The
other is this issue of environmental factors.
Now this, you know, again I'm just going to highlight, when one starts
talking about environmental factors and how they're poisoning us or
disrupting growth or fertility rates it can start to sound a little
bit crazy. Except when you start to actually look at some of the real
data, Data from quality research labs funded by Federal government
funded, not from companies or other sources, that are really aimed at
understanding what the underlying biology is. And for that I really,
we should all be grateful to Tyrone Hayes at UC Berkeley. I remember
way back when I was a graduate student in the late nineties, goodness.
at UC Berkeley. And I remember him, he was studying frogs. He was
talking about developmental defects in these frogs that live in
different waters around it was California, but also elsewhere. And he
identified a substance, which is present in a lot of waterways
throughout this country and other countries. So US and beyond.
Certainly not just restricted to California, which is atrazine. This
is A-T-R-A-Z-I-N-E. Again, this is the stuff of textbooks. And it
causes severe testicular malformations. So again, atrazine exposure is
serious. And what's interesting is if you look at the data, what you
find is that at sites in Western and Midwestern sections of the United
States 10 to 92% of male frogs. These were frogs mind you, had
testicular abnormalities. And the most severe testicular malformations
were in the testes rather than in the sperm. So it's actually the
organ itself, the gonad itself. Now it's very well known now that
atrazine is in many herbicides. And so you know, whereas I would say
in the 80's and 90's the discussion around herbicides and their
negative effects was considered kind of like hippy-dippy stuff or the
stuff you hear about at you know, your local community markets and
these kind of new age communities. Now there's very solid data, from
Federally funded labs at major universities that have been peer
reviewed and published in excellent journals, showing that indeed many
of these herbicides can have negative effects, primarily by impacting
the ratios of these hormones in either the mothers or in the testes,
altering the testes of the fathers or direct effects on developing
young animals and potentially humans. And so you ask, "Well, what
about humans? Frogs are wonderful, but what about humans?" So here are
the data on what's happening and this isn't all going to be scary
stuff. We're also going to talk about tools to ameliorate and offset
some of these effects. One would be, be cautious with Evening Primrose
as well as testosterone creams, depending on whether or not you want
to be more androgenic or estrogenic depending on your needs. But
across human populations, sperm counts are indeed declining, okay? So
in 1940, the average, the average density of human sperm was 113
million per milliliter of semen. That's how it's measured. How many
sperm per milliliter of semen. In 1990 this figure has dropped to 66.
So it went from 113 million per milliliter to 66 million per
milliliter in the United States and Western Europe. So this is not
just a US thing. Researchers also estimated that the volume of semen
produced by men has dropped 20% in that time, reduced sperm count per
generation even further. So between 1981 and 1991, the ratio of normal
spermatogenesis has decreased from 56.4% to 26.9%. So there's a lot
that's happening primarily because of these herbicides that are in
widespread use to reduce sperm counts. And these are going to have
profound effects not just on sperm counts, but on development, sexual
development at the level of the gonads and the brain. Because you need
testosterone to get dihydrotestosterone for primary sexual
characteristics. You need estrogen that's come from testosterone to
masculinize the brain. And of course, we're not just focusing on sperm
and testosterone. You of course also know that many of these
herbicides are disrupting estrogens in a similar way. Or are leading
to hyper estrogenic, excuse me, states which might explain why puberty
is happening so much earlier in young girls these days. So there are a
lot of things that are happening. Now does this mean that you have to
run around and neurotically avoid anything that includes things like
atrazine and should you be avoiding all kinds of herbicides? I don't
know that's up to you. But it does seem that these have pretty marked
effects, in both the animal studies and in the human studies. You
know, you can open up a textbook like the endocrinology textbook and
find things like Vinclozolin. V-I-N-C-L-O-Z-O-L-I-N, which is a
fungicide and it's an anti-androgen. You give it to animals, to rats.
And instead of forming a penis, they don't form a penis. They
basically, it's not that they form a clitoris, they just don't form a
penis. So let's talk about female sexual development.
And as always what we'll do is, we'll talk about the normal biology.
Then we'll talk a little bit about a kind of extraordinary or unusual
set of cases, but we'll talk about them because they illustrate an
important principle about how things work under typical circumstances.
So there is a mutation called androgen insensitivity syndrome. And
understanding how androgen insensitivity syndrome works can help you
really understand how hormones impact sexual development. So here's
how it works. There are individuals who are XY, so they have a Y
chromosome, that are born that make testosterone. They have testes and
they don't have Mullerian Ducts because on the Y chromosome is this
Mullerian inhibiting hormone. However, these individuals look
completely female. And in general, they report feeling like girls when
they're young, women when they're older. But there's something unusual
that's happening in these individuals because they have an XY
chromosomal type and not XX. So what's happening? Well what's
happening is the testes are making testosterone, but the receptor for
testosterone is mutated. And therefore the testes never descend. They
don't have ovaries, they have testes but the testes are internal. And
so typically these individuals find out that they are actually XY
chromosomes. so that you know, their chromosomal sex is male. If you
will. And their gonadal sex is male, but the gonads, the testes are
inside the body. They don't actually develop a scrotum. They don't
make ovaries. And when they don't menstruate around the time of
puberty that's a sign that something is different. And so they never
menstruate around puberty. And if they look into this deeply enough,
what you find is that they are actually XY. They make testosterone but
their body can't make use of the testosterone because they don't have
the receptors. And the receptors are vitally important for some, for
most all of the secondary sexual characteristics that we talked about.
Body hair, penis growth during puberty et cetera. They live fairly
happy lives as females. Although of course they can't conceive, right?
They don't have a uterus, they don't have ovaries. They also in
general, don't produce sperm in quantities enough that they could
actually reproduce with somebody else, although sometimes they can.
And believe it or not, and I'm not going to name names but there are
actually reports of several people, fairly prominent people throughout
history who have had this androgen insensitivity syndrome or people
suspected they did. And the reason to not name names is that, it gets
right to the heart of whether or not they are male or female. How
could you say right? They have XY chromosomes but gonadally they have
testes that are inside. And yet, if you looked at their bodies if you
looked at their faces, you would say almost with certainty that they
appeared female. And that naturally occurring experiment, points to
the fact that testosterone that shows up in the body and impacts the
things that the levels of the receptor has a profound effect on
phenotype. On the external or body plan. So again, we're talking about
this in order to illustrate the principle that in order to have its
effects, a hormone doesn't just have to be present. That hormone
actually has to be able to bind its receptor and take action on the
target cells. And once again, I'll just throw out the example of where
people are using performance enhancing drugs. Although that's a pretty
broad statement, nowadays there's a lot of excitement about the so-
called SARMs. Who are more on the receptor side. And so we'll talk
about this in a future episode. And I just say that as a teaser
because the SARMs and what's happening right now in augmenting sports
performance, both with testosterone directly but also testosterone
derivatives and then also altering things at the level of the receptor
is exceedingly interesting and is revealing to us the many ways in
which hormones can impact brain and body. In ways that we didn't
suspect.
Perhaps the simplest way to understand how estrogen and testosterone
impact masculinization or feminization of the brain and behavior is
from a statement. It's actually the closing sentence of an abstract
that my colleague Neuronal Shaw at Stanford school of medicine
published. Which is that estrogen, again it's estrogen that is
aromatized from testosterone by aromatase, sets up the masculine
repertoire of sexual, and in animals and in humans, territorial
behaviors. So it sets up the circuitry in the brain. Estrogen does
that. Estrogen sets up the masculine circuitry in the brain and
testosterone is then what controls the display of those behaviors
later in life. And I find that incredibly interesting. You would think
it was just testosterone did one thing and estrogen did another, but
it turns out that nature is far more interesting than that. Okay, so
what are some things that impact sexual development early in life and
later in life.
Let's talk about cannabis. Let's talk about alcohol and dare I say
let's talk about cell phones. Something that I never thought I would
ever do, either in this podcast or in the classroom. But, these days
there are really interesting data. And I think you should be aware of
them. First of all, cannabis, marijuana, THC. I realize that there are
now a lot of different variance it's on this. There are a lot of
different strains of cannabis. I personally am not a pot smoker. It's
just not for me. I'm not talking about the moral or legal
implications, in some States it's decriminalized, in other places it's
really illegal and other places it's basically legal. You have to
check, you know where you live and understand the laws. That's not
what this is about. What we do know however, is that with the
exception of one study there are many studies that point to the fact
that THC and other things in cannabis promote significant increases in
aromatase activity. Now pot smokers aren't going to like this,
especially male pot smokers aren't going to like this but it's the
reality. Remember, what you're hearing in the background is Costello
snoring really loud? Should we put them on screen? He's not a cannabis
smoker, but you can imagine why. Come here Costello. Come here buddy,
come here. He's asleep. Come here. He's my [indistinct], there you go.
This dog definitely does not need cannabis. This is his state for most
of the time. He is highly... Oh he's asleep still. So some of you have
asked to see Costello if you're just listening on audio, maybe he'll
gives a [Costello grunts] Oh, okay. We're going to let him get back to
sleep. He's always here, some of you have asked to see him. Costello's
not a pot smoker either. He did have a dog sitter that was a pot
smoker years ago. It was his favorite dog sitter but, I'm not a pot
smoker. Again, no judgment. But here's the deal. That cannabis, and
it's not clear if it's THC itself or other elements in the marijuana
plant, promote aromatase activity. Now, this has been observed
anecdotally where pot smokers have a higher incidence of developing
something I mentioned before gynecomastia, breast bud development. Or
full-blown breast development in males. There may be some women who
want to increase their estrogenic activity. Remember females make
testosterone. It comes from the adrenals, right? They don't have
testes. So it comes from the adrenals and that testosterone can also
be aromatized. Although typically most of the aromatase activity that
we're referring to in these examples is in males. So testosterone can
increase estrogenic activity. So you might say, "Oh you know,
therefore does testosterone reduce sexual behavior? Does it create all
sorts of things that are related to low testosterone?" Not
necessarily, not necessarily. And here's why, estrogen itself in males
and females is important for things like libido and sexual behavior.
I'm going to repeat that. If estrogen is too low in males, it can
actually inhibit libido and sexual behavior. So you don't want
estrogen too high or too low. Whether or not you're male or female.
Now of course in females, estrogen levels tend to be higher than in
males. I'm speaking very generally here. You just think back to the
chromosomal sex. That's what I'm referring to when I say male or
female, although there's nuance there of course. In females, the
testosterone that comes from the adrenals has a powerful effect on
libido and desire to reproduce. And in the next episode, we're going
to talk about how that works and its relationship to birth control,
its relationship to menopause. We're also going to talk about how that
whole thing works in males as well. But cannabis and other aspects of
the marijuana plant can impact levels of testosterone and estrogen by
increasing aromatase. And so people should be aware of that. As well,
there are good data. I was able to find several studies on PubMed,
pointing to the fact that smoking marijuana during pregnancy can shift
the pattern of hormones in the developing fetus, such that it promotes
more estrogenic outcomes. Now earlier I said that estrogen is what
masculinized is the male brain, in utero that's true, but the way that
cannabis seems to work, at least from the studies I was able to
identify is that it promotes circulating estrogen in the body and
therefore can counteract some of the masculinizing effects of things
like testosterone and dihydrotestosterone, on primary and secondary
sexual characteristics. So I mention this because, you know I think
nowadays marijuana use is far more widespread and certainly during
puberty it can have profound effects on these hormonal systems. And so
we'll do another episode, that goes really deep into this. But yes,
cannabis promotes estrogenic activity by increasing aromatase. Almost
everyone can appreciate that drinking during pregnancy, is not good
for the developing fetus. Fetal alcohol syndrome is a well-established
negative outcome of pregnancy. And it's something that there are
cognitive effects that are really bad. There's actually physical
malformation, et cetera. So drinking during pregnancy, not good.
Probably drinking during puberty, not good either. Because alcohol, in
particular certain things like beer but other grain alcohols can
increase estrogenic activity. Now, this isn't just about protecting
young boys from estrogenic activity. It's also protecting girls from
excessive or even hypo estrogenic effects of alcohol in puberty. Now,
many teenagers drink. College students drink and it's important to
point out that puberty doesn't start on one day and end on another
day, puberty has a beginning a middle and an end, but development is
really our entire lifespan. This idea that you know, puberty you know
has this open and close. That's just false. Okay, so we talked about
cannabis. We talked about alcohol. Let's talk about cell phones.
First of all, I use a cell phone. I use it very often. And I do not
think they are evil devices. I think that they require some discipline
in order to make sure that it does not become a negative force in
one's life. So I personally restrict the number of hours that I'm on
the phone and in particular on social media. I only answer email at
particular times of day. But what about the cell phone itself? You
know, when I was a junior professor. I was a pre-tenure early
professor. I taught this class on neural circuits in health and
disease. And one of the students asked me, you know are cell phones
safe for the brain? And you know, all the data point to the fact that
they were. Or at least there were no data showing that it wasn't. I
still don't have the answer on that, frankly. I don't see a lot of
studies about it. I'm not personally aware of any evidence in quality
peer reviewed studies showing that cell phones are bad for the brain
or that holding the phone to the ear is bad or that Bluetooth is bad
or any of that. I'm just not aware of any quality studies. If you are
aware of quality studies, peer reviewed study please reference them,
put them in the comment section. Send them to me, however you like.
I'd love to see them. I'm not aware of them. However, I was very
interested in a particular study that was published back in 2013 on
rats. It was basically took a cell phone and put it under a cage of
rats and looked at basically testicular and ovarian development in
rats and saw minor but still statistically significant defects in
ovarian and testicular development. Since then and now returning to
the literature, I've seen a absolute explosion of studies. Some of
which are in quality journals, some of which are in what I would call
not to blue ribbon journals. Identifying defects in testicular and or
ovarian development by mere exposure to cell phone emitted waves.
Let's just call that, we don't know what they are. And this sounds
almost crazy, right? Anytime somebody starts talking about EMS and
things like that, you kind of worry like, is this person okay? But
look, the literature are pointing in a direction where chronic
exposure of the gonads to cell phones could be creating serious issues
in terms of the health at the cellular level and then in terms of the
output. So the output for the testes would be sperm production.
Swimming speed in sperm is an important feature of sperm health. In
the ovaries it would be estrogenic output. How regular the cycles are.
So in animals, the cycles are a little bit different than in humans.
They don't have a menstrual cycle. They have an estrous cycle, which
is a generally around four days. I think that it's to say based on the
literature, that there are effects of cell phone emitted waves on
gonadal development. The question is, what is the proximity of the
cell phone to the gonads? Now, I've taken the literature as I observe
it. And that of course we'll point you to in the captions. And I don't
like to have my cell phone on and in my pocket, I'm well past puberty,
but nonetheless some of these effects were seen in adult animals.
There are effects now that have been demonstrated in humans. So let's
just talk about a couple of those effects. So a paper published in the
journal, "Clinical Biochemistry" from S. Gander et al. Looked at
hormone profiles in people based on proximity to their phone and
frequency of phone use, where they stored their phone on their body.
Aa well as proximity of where they lived to, I guess they're called
these radio-frequency towers. So the base stations. And they were
looking at effects of radio frequency radiation RFR on human hormone
profiles. And they show significant decreases in cortisol. You might
say, "Well, that might be good." But you need that morning cortisol
bump in order to wake up. Morning cortisol is good. But also thyroid
hormones were significantly reduced. Prolactin in young females,
that's definitely concerning and testosterone levels in males and
females. And so, there are now quite good data showing that being
close to the phone too much of the day and how close is an interesting
question or living near one of these base stations apparently can have
effects on hormone profiles. And when you see a study like this one
should always ask, "Well, what are the other things that could also
have effects on these hormone profiles?" Right? Cause you could
imagine that if you ran the same study of people that live close to a
waterway, or close to a highway where there's a lot of exhaust from
buses and cars, you might see similar effects. So you have to take
these sorts of studies with a grain of salt. But I think it's very
interesting. And given that the last time I looked into these data
were way back when I was a junior professor and there was like one or
two studies that I could find. One of the studies pointed to increases
in testosterone in rats, where they were had close proximity to these
radio-frequency radiation waves. And then in the other case, it showed
decreases in testosterone. So there really wasn't any conclusion to
takeaway from that. Now, there's pretty impressive amount of data
pointing to the fact that there are effects of these things on
hormones. I don't know what to do with that information. I'm not going
to stop using my phone but, in light of the work from Tyrone Hayes and
others looking at sperm counts and looking at the decrease in
testosterone levels and sperm counts and fertility over the last 20,
30 years, perhaps it's you know, not surprising. Although there again,
cell phones and smartphones have really been in prominent use mostly
within the last 10 or 11 years. And so it's hard to explain all of
those declines simply on the basis of cell phone use.
There's some interesting effects of hormones that actually you can
observe on the outside of people, that tell you something about not
just their level of hormones, but also about their underlying
genetics. And these relate to beard growth and baldness. And it's
fascinating. The molecule, the hormone dihydrotestosterone, made from
testosterone, is the hormone primarily responsible for facial hair,
for beard growth. As well, it's the molecule, the hormone primarily
responsible for lack of hair on the head, for hair loss. So how does
that work? Well, DHT circulates in the body and it binds to DHT
receptors in the face to promote hair growth. But it binds to DHD
receptors on the scalp to promote hair loss. Not incidentally, the
drugs that are designed to prevent hair loss are 5-alpha-reductase
inhibitors. So remember 5-alpha-reductase from the Guevedoces? Well,
the people that discovered the Güevedoces, went on to do a lot of
research on the underlying biochemistry of this really interesting
molecule dihydrotestosterone. They identified 5-alpha-reductase. and
5-alpha-reductase inhibitors are the basis of most of the anti-hair
loss treatments that are out there. And so there's some interesting
things here. First of all, the side effect profiles of those
treatments for hair loss are quite severe in many individuals.
Remember DHT is the primary androgen for libido, for strengthened
connective tissue repair, for aggression. Even if that aggression of
course is held in check, but just sort of ambition and aggression is
related to dopamine, but within the testosterone pathway, less so pure
testosterone, although pure testosterone has its effects. But DHT is,
at least in primate species including humans, is the dominant androgen
for most of those sorts of effects. And if you look at somebody,
everyone can predict whether or not they're going to go bald based on
looking at their, we're always taught our mother's father. So if your
mother's father was bald, there's a higher probability that you're
going to go bald. The pattern of DHT receptors on the scalp, will
dictate whether or not you're going to go bald everywhere or just in
the front or the so called crown type baldness. And the density of the
beard tells you about the density of DHT receptors. Now this varies by
background, by genetic background. And actually around the world
nowadays, because people travel and people form couples and have kids
with so many different people of different mixed cultures. You're
seeing this starting to disappear. But there are areas areas of the
world where all the men seem to have the same pattern of baldness,
like a strip of baldness down the center, with hair still on the sides
and and full beards. That's because these patterns of DHT receptors
are genetically determined. Elsewhere, testosterone levels can still
be very high, DHT levels in the blood can be very high and yet people
will have very light beards or no beards. And that's because they
don't have a lot of DHT receptors in the face. And in still other
cultures you'll see people with huge beard, tons of beard. Their
beards are growing all the way up to their eyes and they have huge
heads of hair. And that's because they have a lot of DHT receptors on
the face and not on the scalp. So there are a lot of effects of DHT
that you can just see in male phenotypes. And it's interesting that
these hair loss drugs that are, or to prevent hair loss drugs, are
directly aimed at preventing the conversion of testosterone into
dihydrotestosterone. And that's why they to some extent prevent hair
loss, but also to some extent have, a bunch of side effects that are
associated with low DHT. Along these lines there's a particular sports
supplement that a lot of people use called Creatine. Creatine, now
there's a lot of research showing that Creatine can bring more more
water into the muscle.
It can support strength. It does a number of other things. Might even
have some important cognitive promoting. Cognitive enhancement
effects, although mild. The studies there show that it can be
significant. Some people, not all it's more anecdotal, report that
creatine promotes hair loss. It differs by individual. For some people
that's true, for others no. But yes it does appear, based on the
studies I was able to find on PubMed, that creatine does promote
5-alpha-reductase activity and therefore the conversion of
testosterone into dihydrotestosterone. And so it makes sense that it
might promote some degree of hair loss, as well as beard growth, as
well as the other effects of DHT. I recall in junior high school and
middle school, going home one Summer it was seventh grade, coming back
in the eighth grade and a kid that I knew that I was friends with,
went from being like a young kid to, he was like a grown man, he had a
full beard. It was amazing. It was like he would completely
transformed. And in puberty as I've said before, is without a doubt
the most accelerated rate of development that we will go through at
any point in our lives. Even faster than infancy just in terms of the
huge number of different cognitive changes and physical changes. Not
surprisingly that same individual was mostly or bald by his early
twenties. And that's because he must have had just exceedingly high
levels of DHT. I also played soccer with this kid and he was basically
like dribbling past everybody. It who was like a grown man, playing
soccer with a bunch of little kids. Full beard you know, bald at 20.
And so the rate of maturation, the rate of aging is very interesting.
It's hard to know rate of aging. There's some genetic tests that now
can allow you to do that. Things like Horvath Clocks and things of
that sort. Beautiful work of David Sinclair at Harvard and others has
pointed to this. The speed of entry and exit from puberty might be,
I'm putting it out there as a hypothesis. Might be an interesting
window, into how fast one is going through their aging or
developmental arc. Because development of course, doesn't just start
at birth and end after puberty. It continues your entire life. So I
think it's interesting. You will often see that people, boys and
girls. I should say boys or girls, will develop secondary sexual
characteristics at different rates. And sometimes it's sequential. You
know you might see a kid will, she'll grow very tall or she'll have a
big growth spurt, but then breast development will come a little bit
later. And then other features will come a little bit later. You can
also see this in boys. The person that I referred to earlier, my
friend that developed a full beard, you know, went bald. He was also
quite muscular, he was a great athlete. So he went through puberty
exceedingly fast. Other people go through it more slowly. Some people
will go through puberty at age 14, but they won't start to accumulate
facial hair until much, much later. Or their voice will change first,
very early. And then they won't get the other secondary sexual
characteristics until much later. And so, we don't really know how
that impacts or relates to overall trajectory or rate of aging. But
it's an interesting thing to think about for each and every one of us.
I'm going to offer you the opportunity to do an experiment today,
while listening to the podcast. But first I want to tell you a story
about hyenas, professional baseball and clitoris's the size of
penises.
So when I was a graduate student at UC Berkeley, we had a professor in
our department, phenomenal scientist named Steve Glickman. Steve
Glickman, had a colony of hyenas, spotted hyenas that lived, within
caged enclosures of course, in Tilden Park behind the UC Berkeley
campus. The enclosures are actually still there. I run past there
fairly often. The hyenas are no longer there. This was a Federally
Funded field station. These animals were brought over from Africa or
were bred there. And the reason why they were hyenas in Tilden Park,
enclosed in Tilden Park. Was because hyenas exhibit an incredible
feature to their body, their hormones and their social structure.
Hyenas, unlike many species, have a situation with their genitalia
where the male penis is actually smaller than the female clitoris. And
I should say that the male penis itself, having seen a fair number of
hyena penises, is not particularly small. Which means that the hyena
clitoris's are extremely large. This was well known for some time. It
turns out that in these spotted hyenas the females are dominant. So
after a kill the females will eat, then they're young will eat. And
then the male hyenas will eat. As well, when the female hyena gives
birth, she gives birth, not through the vaginal canal that we're
accustomed to seeing, but through a very enlarged clitoris's like
phallus. Although it's not a phallus, it's a clitoris. And it
literally splits open. So many fetuses die during the course of hyena
development and birth. These animals have this, what could only be
described as a very large or giant clitoris. Although for a hyena it's
not giant, it's normal. And it splits open and the baby actually comes
through. The baby hyena actually comes through the tissue and it's
it's a very traumatic birth. A lot of tissue is torn away, et cetera.
And as I mentioned, a lot of baby hyenas die. It was a mystery as to
how the female hyenas have this we'll call it masculinization, but
it's really a androgen jet. Excuse me, androgenization of the
periphery. Of the genitalia. And it turns out, through a lot of
careful research done by Steve Glickman, Christine Drey and others.
That it's androstenedione. What is essentially a pro hormone to
testosterone? It's androstenedione at very high levels that's produced
in female hyenas that creates this enlargement of their genitalia. So
if you want to read up on androstenedione. Androstenedione is made
into testosterone through this enzyme 17-beta-hydroxy steroid
dehydrogenase it's a complicated pathway to pronounce. It's a fairly
straightforward pathway biochemically. You may recall during the 90's
and 2000's there were a lot of performance enhancing drug scandals, in
particular in Major League Baseball. And it was purported, although I
don't know that it was ever verified. But it was purported that the
major performance enhancing drug of abuse at that time, in particular
players whose names we won't mention but you can Google it if you want
to find out. Was androstenedione. And I actually recall long ago, when
you could buy androstenedione in the health food stores. And so it was
sold over the counter. So a lot's changed since then. But it's
interesting that these hyenas, with these highly androgenized
genitalia accomplish that through high levels of androstenedione in
the females. Now if that's unusual, what might be even more unusual is
that a graduate student that I was working with at the time.
Alongside we didn't share research. Her name was Nicola Sitka. She is
actually a trained behavioral, animal behavioral expert. She had
trained ferrets for that show the "BeastMaster." And she had trained
wolves for television shows and was a dog trainer. She had these two
large dogs that, unlike my dog would actually listen to her when she
would give them commands. A remarkable scientist. She was studying a
species of mole that also lived in Tilden Park. People are going to
start to wonder about Tilden Park, what's in Tilden Park? But this
particular mole that lived there had testes for part of the year and
had the capacity to trans differentiate its testes into ovaries in
order to balance out the ratio of males and females in the population
to keep reproduction at appropriate levels for that certain
population. So some animals are actually able to adjust whether or not
they have androgenized or estrogenized gonads, in order to adjust the
ratios of offspring or the males and females in therefor promote
offspring. And the last little anecdote about this, which is also
published in the scientific literature, which is weird but I do find
interesting.
Hormones are so fascinating, they're just incredible to me is going
back to the marijuana plant. You know, the marijuana plant has these
estrogenic properties. And I asked a plant biologist whether or not
this was unusual. And I asked because there's all this stuff out there
about, "Oh, you know, Soy does this. And these plants are highly
estrogenic, et cetera." Although we should probably point out that a
lot of factory meats are also estrogenic. So this isn't a meat versus
plants thing. But this plant biologist told me, "Oh yeah, there are
plants that make what is essentially the equivalent of testosterone
like pine pollen as it looks a lot like testosterone. And there are
other plants that make what is essentially estrogen. And I said,
"Well, why would they do that?" Well and you know plants, at least as
far as I know, don't have a consciousness. They don't have a brain.
They don't have neurons even but, his answer was fascinating. He said
that, one of the reasons why some plants have evolved this capacity to
increase estrogen levels in animals that smoke, not smoke it but then
animals that consume them. I'm guessing that animals aren't smoking
marijuana. Although I don't know, send me the paper if you've heard of
this. Is that plants have figured out ways. They've adapted ways to
push back on populations of rodents and other species of animals that
eat them. So plants are engaged in a kind of plant to animal warfare
where they increase the estrogen of the males in that population to
lower the sperm counts, to keep those populations clamped at certain
levels so that those plants can continue to flourish. Even if those
animals are reproducing very robustly. And I find this just
fascinating. And hormones therefore, aren't just impacting tissue
growth and development within the individual and between the mother.
Remember the placenta is an endocrine organ, and the offspring, but
plants and animals are in this communication. And today we're in this
communication, I'm telling you that there are certain herbicides that
humans are using for which there's very good data, are disrupting the
endocrine pathways. And so it's fascinating that humans and other
animals, we're always in this interplay with plants and the other
things in our environment. And hormones and adjusting the hormone
levels of animals and plants is one way in which the environment kind
of pushes back or pushes forward if you will, in terms of promoting
their well-being and longevity, as well as you trying to promote your
wellbeing and longevity. If anyone wants to see the incredible paper
by Steve Glickman and colleagues. It was published in the proceedings
of the national Academy. First in 1987, that's Glickman et al. That
was the hypothesis that it was androstenedione . And then if you just
Google Glickman hyenas science magazine, there's a beautiful cover
article and feature all about that important discovery, it's a
fascinating one. And I should mention also that those discoveries,
both the moles and the hyenas weren't just impactful for the world of
animal behavior and endocrinology, they've also strongly impacted
understanding of conditions that show up in the clinic, which we
haven't talked about today. Which is actually pseudo hermaphroditism.
Occasionally babies will be born where it is unclear, if they are boys
or girls based on the genitalia. And this has a very important ethical
and other issues. Do you raise them as a boy or a girl? It's not super
uncommon for this to happen. And there have been terrible cases where
people have gone against the chromosomal sex. And the person was very
unhappy with the the choice that their parents had made for them.
There were also cases where they've gone with a chromosomal sex and
the person was very happy about the outcome. There've been cases where
they've been treated with hormones and there been cases where they
have not been treated with hormones. It's a complicated literature and
it has to be sorted out on kind of a case by case basis, but it is
something that does happen. And the studies on androstenedione in
hyenas and in these very interesting moles, pseudo-hermaphroditic
moles that live in Tilden Park, have impacted not just the science but
the therapeutics around those important issues.
So now last but not least, I want to discuss the effects of hormones
while you and I were separately in utero and the effects that that had
on who we are, who we select as mates. So mate choice, sexual
preference. And all other aspects of what you would call sexual
development. Now this is something that's gotten a lot of popular
press and it has to do with how exposure to androgens in particular
while we were in utero, impacted whether or not people report as
homosexual, heterosexual, identify as male or female. I'm very
familiar with this work because I was a graduate student in the
department that first published this work and I'm an author on the
paper. I was not the main driver of the work, but I was involved in
the work. And I certainly know the people that did this work. First it
starts with a story. There was a researcher who's still going now. His
name is Dennis McFadden. I believe he was at UT Austin back then. And
he was studying the auditory system. And people would come into his
clinic and he would, or his laboratory. And he would look at hearing
and he would explore different aspects of what they call the
psychophysics of hearing and understanding hearing thresholds and
frequency thresholds. And he made several observations. And those
observations were that young males tended to have what are called auto
acoustic emissions, more often than young females did. Auto acoustic
emissions, as the name suggests, are the ears actually making sounds.
Now these sounds have to be picked up by a special apparatus, because
they can hear into that frequency. But it turns out that your ears
don't just take sound waves and convert them into this thing we call
hearing. But they also in some cases make sound. So your ears are
making sounds. Strange right? So it turns out that there's a sex
difference in auto acoustic emissions. It turns out also that people
that self-report as lesbians, they also have auto acoustic emissions
significantly more than females that don't self-report as lesbian. And
Dennis noticed this and published this. And it was an important
discovery because it was one of the first discoveries that pointed to
the fact that there are sex differences in biology that are
independent of sex. I mean, this is hearing and auto acoustic
emissions. And just to really illustrate what that. What the former
problem was and why this study was so important? You know, a lot of
people had explored for instance whether or not, homosexuals had lower
testosterone for instance in males. And actually the result often was
the opposite. That gay men or men that self-report is gay, often had
much higher testosterone. And those studies then became controversial
because people said, "Well, sexual behavior can relate to
testosterone," et cetera. And so it became very controversial. And
then there were some studies that attempted to look at the equivalent
phenomenon in people that self report as lesbian. Or self-report as
heterosexual. And so it became very complicated. But this was an
identification of a phenomenon, auto acoustic emissions, that was
independent of anything that had to do with sexual or even social
behavior. 1998 rolls around. And I'm a graduate student at UC Berkeley
and a guy by the name of Mark Breedlove. Kind of an ironic name, given
that he worked on. He worked and still works on sexual dimorphism in
the brain and in the spinal cord and nervous system. And Mark, who's a
phenomenal scientist comes running down the hall. I'll never forget
this. And he said, "Give me your hands." I was like, [indistinct].
He's like, "Give me your hands." And he pulls out a ruler and he
starts measuring my fingers. And he takes down a couple of
measurements and then he goes away. And I was like, "What was that?"
Well, I was in a course that Mark was teaching at that point. And soon
after, we did a study that Mark directed exploring the finger length
ratios. And I'll explain what those are. Of males and females, and
people that self-reported as homosexual or heterosexual. So let's just
get to the basic, what we'll call sex differences first. These are
averages. I want to point out. Anytime you get into this kind of
topic, people assume it's causal, but it's not causal. These are
averages that I'm about to report. It is the case that the ratio of
what's called the D2 to D4 digits. So the D2 is your index finger. So
your thumb is D1. Then D2 would be your index finger that you would
point with. Middle finger is D3, which you whatever with. And then D4
is the so-called ring finger. Okay and D5 is the pinky. It is the case
that the D2 to D4 ratio is greater in self-reported females than it is
in males. What does that mean? It means that digit D4 and D4 are more
similar in length in females than in men males. And that effect is
particularly, excuse me, pronounced on the right hand. Although not
always, okay? And it does not have to do with handedness. This D2 to
D4 difference has to be measured correctly. You can't just look at
somebody who's hands and say, "Oh, their ring finger and index finger
are very similar. And therefore they are female you know. Or they were
exposed to very little testosterone in utero." You can't look at
somebody and see that their index finger is much shorter than their
ring finger and say, "Oh, they must've been exposed to a lot of
androgen." You have to actually measure it and you have to measure it
correctly. You have to measure it from the base of the finger where
there's that first crease, all the way to the tip past the. You can't
include the fingernails. If you're growing fingernails, it'd be
logical here folks. So you can't normally see it from the back of the
hand. Although, I don't know if this'll show up here but if you look
at the back of the hand sometimes you can see it. You know, in my case
for instance. Let me see if I can do this. So my D4 is a little bit
longer than my D2. In some people it's more pronounced and that's on
my right hand. On the other hand, the difference actually is far less
pronounced. Is it's a little bit. it's a little bit pronounced there,
but not so much okay? So that's sort of the typical ratio that you
would see. It turns out that in mice and in humans, the more androgen
that you were exposed to in utero, the smaller the D4 D2 ratio.
Meaning that the ring finger tends to be slightly longer than the
pointer finger. And in females because they're exposed to less
androgen in utero typically. Then those fingers tend to be more equal
in length. And these are subtle differences and these are averages. I
invite you to look up the paper. This was published in Nature in 2000
and it's been replicated six times. Now, here's where it gets even
more interesting. And potentially precarious, so we're going to step
cautiously here. If you look at the finger length ratios of men that
self-report as homosexual, they have either the typical male pattern
of D2 to D4 ratio or a hyper masculinized D4 to D2 ratio. Now this
can't be something that's established or modified by behavior. This
has to be something that was established in utero. And in fact, it's
present at birth okay? So it completely divorces the interactions
between hormones and behavior. And that's an important theme that
we've been talking about. And we're going to talk about even more.
Next episode is that hormones impact behavior but behavior also impact
hormones. But this is a case of hormones impacting what really should
be considered a primary sexual characteristic. Because it doesn't show
up in puberty, it shows up before puberty. It's actually established
in utero. And in people that self-reported lesbians. And I remember
going out there and collecting these data with, with the collaborators
on this work. Again, I wasn't the main driver on the work. But I
participated in some of the analysis. People that self-report as
lesbians also tend to have a smaller D2 to D4 ratio. So this is
consistent with the auto acoustic emission study that Dennis McFadden
had published. And it points to the fact that early exposure to
androgens may have an impact, not just on androgenization of the body
plan, but also separately on sexual preference. Now, this raises all
sorts of interesting questions about biological basis of sexual
preference. I'll tell you about another study. A guy named Simon LeVay
who was at UCLA.
Who trained under Hubel and Wiesel. If any of you remember early
episodes on "Plasticy," David Hubel and Torsten Wiesel my scientific
great-grandparents won the Nobel Prize for discovery of critical
periods for brain plasticity. They defined some of the most important
aspects of how we see and brain plasticity. Simon LeVay trained with
them. And then Simon went on to discover that in the brains of people
that self-report homosexual there is a brain difference. And the brain
difference is in an area called the Interstitial Nucleus of the
Anterior Hypothalamus. So it's the INAH. And so there are published
reports. That was published in Science. The other work I refer to as
published in Nature, and then replicated no fewer than six times. And
the McFadden results that point to strong biological correlates of
mate choice, of sexual preference. And these tie directly to things
like androgenization or estrogenization. Meaning we could call it
maleness or femaleness, but that's sort of tricky territory. Because
of the way that we described the huge range in which sex can be
defined earlier. So, if you want to measure your D2 D4 ratio you're
welcome to, but you also have to understand that it's not predictive
of anything, right? It's just a window into the possible androgen
exposure that you had early in life. There are plenty of men who
report themselves as heterosexual who are out there who have similar
or have D2 D4 ratios to females. And there are plenty of females whose
index fingers are shorter than their ring fingers. And they're
perfectly happy where they say they're perfectly happy. And we are
inclined to believe them being heterosexual. So there's variation. In
fact, Mark tells a really good joke. If you want to know whether or
not somebody is homosexual or heterosexual, simply look at their
hands, look at their D2 D4 ratio and guess heterosexual. And you'll be
right 96% of the time. Because 96% of the time people report
themselves as heterosexual on average. Those numbers might be
changing. So the joke really is a joke on science because, that falls
within the realm of statistical significance. And yet it really
illustrates the fact that none of this is causal. But it's nonetheless
very interesting because it means that hormones are organizing the
brain early in development in ways that can potentially impact same or
opposite sex partner choice later in life. Now of course, there are
other things that can impact opposite sex or same-sex partner choice
later in life. The study did not look at people who reported bisexual.
There hasn't been a lot of studies on that yet. One thing that's very
interesting, for which there are some good scientific data but there's
also some controversy is that, it appears that the probability of a
male human self-reporting as homosexual, increases with the number of
older brothers that he has.
Now, that doesn't mean if you have an older brother or even if you
have 10 older brothers, that you are sure to self-report as
homosexual. But statistically it becomes more likely that somebody
will with each successive older brother that they have. And the idea
that starting to emerge, in the developmental neuroendocrinology
landscape is that there's a record within the mother of how many male
fetuses she's carried, because male fetuses are secreting certain
things, dihydrotestosterone, other things, that can feed back on to
the genome. So these could be epigenomic effects or onto the placenta
itself, so that there's a higher probability in subsequent pregnancies
that offspring will self-report as homosexual. So it's a fascinating
area of biology. And as you've noticed today, none of this deals with
the current controversies around gender and how many genders and sex,
et cetera That's a separate conversation that is by definition
grounded in the kind of concepts we've been talking about today and
needs to take place, taking into consideration all of the aspects of
sex and the effects of hormones, both on the body, on the brain. We
didn't talk a lot about spinal cord, but we will in the next episode.
But we can just say on the brain and the periphery, early effects,
late effects, acute effects, meaning effects that are very fast of
levels of hormones going up or down. Something that absolutely happens
during and across the menstrual cycle. As well as long-term effects
like the effects of these hormones on gene expression. So today, as
always, we weren't able to cover all things related to sex and
hormones and sexual differentiation or development. There's no way we
could. But we have covered a lot of material. We talked about some
effects of environmental toxins. We talked about potential effects of
cell phone radiation. Something I never thought that I would be
talking about, especially not in a podcast. But for which there are
interesting emerging data. We talked about considerations about
Evening Primrose Oil and its estrogenic effects. About Creatine and
its pro DHT effects. About cannabis, alcohol. About plants exerting
warfare on animals by increasing aromatase. The conversion of
testosterone to estrogen. We talked about hyenas with giant
clitoris's. And we talked about moles that can revert from having
ovaries to testicles. And throughout this Costello has been snoring
nonstop. He missed all of it. Although he might be learning it in his
sleep for all I know. And I do understand it's a lot of information, a
lot of detail as always. I just want to remind you, you don't have to
absorb all the information at once. Next episode, we are going to be
talking about the science of sex, the verb, actual reproduction.
We're also going to be talking about effects of hormones on various
aspects of behavior and ways to modulate hormones, through the use of
behavior, supplementation. Also we'll touch on diet and nutrition a
bit. And we're going to talk about interactions between those things
and behavior, as they relate to important themes like sex and
reproduction. Like workplace performance. Like motivation and drive
and even anxiety. There's a very interesting relationship between
hormones and anxiety and the desire to explore novelty. So just to
remember as we go forward that, hormones affect behavior and behavior
affects hormones. But that doesn't mean that cutting off your index
finger will increase your testosterone. Many of you have asked how you
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music]
HubermanLab #Testosterone #Estrogene
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Links:
* Mood Meter: https://moodmeterapp.com/
* NSDR: https://www.youtube.com/watch?v=pL02HRFk2vo
* Cell Phones & Hormones: https://pubmed.ncbi.nlm.nih.gov/22138021/
* Finger Length Ratios & Hormones/Sexual Orientation:
* https://www.nature.com/articles/35006555
* https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2940503/
* LeVay Study in Science Magazine on Sexual Orientation Brain Dimorphism:
* https://science.sciencemag.org/content/253/5023/1034
Timestamps below.
00:00:00 Introduction
00:06:47 Announcement: Mood Meter App Works Again
00:08:00 Maximizing Learning from the Podcast
00:10:00 New Non-Sleep Deep Rest Protocol, Spanish Subtitles
00:11:35 Sexual Differentiation: Hormones, Neurons & Behavior
00:14:15 Hormones Basics
00:15:26 Sperm Meets Egg, Chromosomal Sex, Gonadal Sex,
00:17:50 Y Chromosome Inhibition of Feminization
00:19:00 Placenta Is An Endocrine (Hormone-Producing) Organ, Adrenal Testosterone
00:19:45 Hormonal Sex, Morphological Sex
00:21:04 Hormones Fast & Slow, Sex Steroids Can Turn On Genes
00:23:06 Masculinization, Feminization, Demasculinization, Defeminization
00:23:42 Primary Sexual Characteristics: DHT Drives Penis Development
00:27:03 Secondary Sexual Characteristics
00:27:43 Penis Sprouting: Guevedoces
00:31:25 Estrogen, NOT Testosterone, Masculinizes The Brain
00:33:15 Breast Development In Males: Aromatase; Puberty, & Steroids in Athletes
00:34:50 Estrogen Powerfully Controls Brain Development In All Individuals
00:35:19 Avoiding Hormonal Disruption In Children & Adults: Specific Oils, Creams, Etc.
00:39:00 Environmental Endocrine Disruptors, Sperm Count Decline, Vincloziline
00:44:20 Androgen Insensitivity Syndrome: Hormones Need Receptors, SARMS
00:48:41 Estrogen Establishes “Masculine” Brain Circuits, Testosterone
00:49:42 Cannabis, Alcohol: In Babies, Puberty & Adults
00:56:25 Cell Phone Technology: Effects On Hormones, Ovaries, & Testicles
01:02:33 Beards & Baldness Patterns Around the World, DHT, 5-alpha-reductase
01:06:39 Creatine & DHT/Hair Loss
01:08:20 Predicting Aging Rates By Pubertal Rates
01:10:04 Hyenas, Baseball, & Hypertrophied Clitorises: Androstenedione
01:14:26 Intersex Moles
01:15:40 Marijuana Plants, Pollens: Plant-To-Animal “Warfare”
01:20:08 Finger Length Ratios, Prenatal Hormone Exposure & Sexual Orientation
01:29:13 Brain Dimorphisms with Sexual Orientation
01:32:00 “Older Brother Effects”: Male Fetuses Might Change Mothers & Subsequent Brothers
01:35:06 The Path Forward & A Warning
01:35:55 Support & Your Questions
Please note that The Huberman Lab Podcast is distinct from Dr.
Huberman's teaching and research roles at Stanford University School
of Medicine. The information provided in this show is not medical
advice, nor should it be taken or applied as a replacement for medical
advice. The Huberman Lab Podcast, its employees, guests and affiliates
assume no liability for the application of the information discussed.
[Title Card Photo Credit: Mike Blabac https://www.blabacphoto.com/]