How Hormones Shape Sexual Orientation & Behavior | Dr. Marc Breedlove

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The larger the number of older brothers that a male has, the higher the probability that he is gay. >> It’s been seen over and over. I mean, it’s it’s really one of the u rock solid findings in human sexuality. So, the way to emphasize the difference is if a baby boy is born today, um if if he has no older brothers, his odds of being gay when he grows up is about 2%. Right?

Pretty low. But if he had one older brother, his odds go up by a third. Okay, 2. 6. And if he has two older brothers, they go up a third again.

All right, now we’re at 3. 5. It turns out you got to have like a dozen older brothers just to have a 50/50 chance. Welcome to the Huberman Lab podcast, where we discuss science and science-based tools [music] for everyday life. I’m Andrew Huberman and I’m a professor of neurobiology and opthalmology at Stanford School of Medicine.

My guest today is Dr. Mark Breedlove. Dr. Mark Breedlove is a professor of neuroscience at Michigan State University, and he is an expert in how hormones shape the developing brain, in particular, how they influence sexual orientation. As you’ll learn today, the amount of testosterone that a fetus is exposed to while in the mother has a profound impact not only on the ratio of finger lengths, yes, you heard that right, but it also plays a meaningful role in sexual orientation.

And in fact, there’s a correlation there between finger length ratios and sexual orientation. Now, as wild as that may seem, that result has now been confirmed many times over in humans and in animals. And today, you’ll understand why. You’ll also learn that every time a woman is pregnant with a male, there’s a biological trace of that which biases the likelihood that her next male offspring will be either heterosexual or homosexual. Now, I know this sounds really out there, but these are extremely solid biological findings for which the mechanisms are now understood for both animals and humans.

It turns out that the hormones we are exposed to while we are in the womb shape not only the preference for whether somebody is attracted to males or females, but also an aversion to the opposite. Meaning there appears to be the formation of circuits for being attracted to one sex and not attracted to the other. Today you’ll also learn how hormones impact the amount of rough and tumble or social play that kids engage in, the interplay between nature and nurture in shaping male versus female differences and sexual orientation. Dr. Breedlove is one of the long-standing pioneers in this field of how hormone shape brain development and psychology.

We approach these questions through the lens of biology and statistics. So today’s is not a political discussion. Instead, it’s a discussion about what is known and what is still not known about this profound aspect of our species. Oh, and we also talk about gay rams. Yes, that’s a real thing and it has important implications for everything we’ve mentioned thus far.

By the end of today’s episode, you’ll surely think differently about the relationship between hormones and brain development, nature and nurture, and romantic partner choice. Before we begin, I’d like to emphasize that 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 to the general public. In keeping with that theme, today’s episode does include sponsors. And now for my discussion with Dr.

Mark Breedlove. Dr. Mark Breedlove, welcome. >> Thank you. I’m delighted to be here.

It’s very exciting. >> Been 25 years since we stood in the same physical space. >> I know. How can that How can that be possible when I I feel like, you know, just saw you a few days ago, but then >> Well, you look great. Uh you look the same.

So, uh we can talk longevity protocols at the end, but >> I’m trying to have a blonde look in my hair apparently. So, >> well, um, I’ve wanted to have you on this podcast since I launched it because you work on one of the most interesting things in the world, which is how and why people become who they are and how hormones play a role there, how genes play a role there. >> If you’re willing, I’d like to jump from the high dive to the deep end first. Right off, >> let’s talk about this fingerlength ratios sexual orientation study that >> you published and somehow I landed on that paper. That’s not why I want to talk about it.

I want to talk about because it’s an incredibly interesting set of findings. Other people have done the sameish experiments and there’s a whole context there about how hormones influence sexual orientation independent of behavior. >> We need to step back a little bit for the context. Uh, one thing that your listeners might not know is, you know, in the year 2000, there was still a lot of people who regarded um, same-sex orientation as a choice, a lifestyle choice. That was the the political combination of words that meant you could disapprove of people u because they were attracted to the same sex.

Of course, I’m I’m at Berkeley. I I didn’t have any truck with such notions at all. and and and I’ve always been convinced that sexual orientation is not a choice. And there’s a exercise I do in class where I ask so I’m going to put you to it now. So remember the first time you had a crush, >> right?

It might have been someone on TV, might have been someone a playground, etc. So think about it and I I want you to tell me about how old you were at the time in a moment. >> My guess is it was before puberty. >> Yeah, I was six. So and I hit puberty somewhere starting around 14.

So, so it had nothing to do with puberty, right? It was this thing that happened and and I’ll I’ll share my experience. So, so I’m about six or seven. I couldn’t have been more than seven. Uh, and Marilyn Monroe is on TV.

I’m dating myself. And there’s a closeup, you know, with that face and the and the mole, etc. And afterwards, I’m just so agitated. I don’t, you know, I don’t I and I know nothing about sex. I remember I had a hard time going to sleep.

So, it was like something about this was really agitating me and I didn’t choose to have that reaction and my guess is that whatever sex you had your first crush on, that’s the one you were going to be attracted to the rest of your life. >> Yeah. It’s been constant. >> Yeah. Well, so so so this idea that it was a choice that always just seems so absurd to me.

On the other hand, um, even though, you know, I’ I’ve been doing animal research with giving hormones early in life and seeing what it did to the nervous system, etc. Um, and every time I wrote an NIH grant, I said, well, you know, the effect of early hormones may be important for human behavior. But to tell you the truth, I never actually believe that, right? It was just I I just wanted to justify be because it seemed to me that we are so sensitive to social influences and we have this long stretch of time where we’re, you know, our brains are still growing at a fetal rate of growth until at like 9 or 10 years of age and we’re taking in so much information and and think of what a what a heterosexual world it is, right? I mean, all those Disney movies with Prince Charming and etc.

Uh, and so it always seemed to me that that social learning would be more than enough to explain why 95% of people are straight. But that doesn’t mean that was a choice. And it doesn’t mean that they would even be aware of what the social influence was. So, so my example is I speak English. It’s, you know, I’m hopelessly monilingual only language I speak.

Well, I don’t remember learning English and I certainly didn’t choose to learn English, but I’m sure that it’s English because of social influences, right? So that was where I stood on the question of sexual orienta