Carole Hooven: ‘It’s obvious that men are much more driven by sex than women’

The Harvard professor of evolutionary biology has published a book linking testosterone to behavioral differences between the sexes

Author Dr. Carole Hooven.
Author Dr. Carole Hooven.

Evolutionary biologist Carole Hooven says that “sex is real… it’s biological. It’s in your body. It’s not in your head.” Hooven has served as the co-director of undergraduate studies in Harvard University’s Department of Human Evolutionary Biology, and she is aware that such statements might be seen as shocking in certain environments. “Your body’s plan for gamete production has a lot of implications, but it doesn’t dictate anyone’s value or rights, and it shouldn’t… in some places, sex is important. Like maybe in sports. Maybe in prison cells. Maybe in the data that we collect about sexual violence,” she says.

Hooven believes that it is important to be able to talk about sexual differences in order to make the best decisions, and that it is necessary to include data from scientific research in such discussions. With that in mind, Hooven wrote the book T: The Story of Testosterone, the Hormone that Dominates and Divides Us. In it, she draws on her experience as a professor of human evolutionary biology to analyze studies about the role the hormone plays in sexual differences in both humans and animals; she combines that data with personal stories to support her thesis.

In a video call, the professor says she understands, in part, misgivings about certain claims made in the name of science. “There is obviously a history of science being misused as a justification. You know, if I say that I think women have a nurturing instinct that is stronger than in men, maybe some politicians will come out and say, well, then women need to be the ones to stay home with the kids. No, that’s not how it works. So, that’s the connection I want to break: the link between what is natural and what society should be,” she argues. “I understand the resistance to just getting the facts out, but the answer to that problem is not to lie to people about reality.”

Question. Do you believe that gender roles arise from biological preconditions, that they are not entirely created by culture?

Answer. So, nothing that is as cultural and complex as gender roles is totally social or totally biological. Every culture has something like sex roles. Gender is a complicated term, so for now I’m just going to say sex roles. So, standards and norms of behavior for males and females, every culture has them. And there are some very strong and consistent norms across cultures that also are consistent with what we know about biological differences in humans and non-human animals. All cultures have norms about sexual behavior and regulating sexual behavior to some extent, and most incorporate greater latitude for male sexuality than for female sexuality. So, that’s something that is fairly consistent across cultures that I think has a strong biological influence.

But culture is extremely important in terms of shaping how sex differences that may have biological roots manifest themselves within a society. There are patterns that are very basic, like those differences in sexual behavior that are never reversed in any culture. Like, there’s no culture that I know of where female promiscuity is celebrated and encouraged, and male promiscuity is sometimes punished severely. That just doesn’t really exist. And although there’s variation in standards for female promiscuity and variation in standards for male promiscuity, you never see that basic pattern reversed.

That was just an example for sexual behavior. But when it comes to aggression and norms for the expression of male and female aggression, there are patterns there that aren’t reversed either. For example, patterns where female physical aggression is celebrated and rewarded and male physical aggression would be punished. So, I think those very basic patterns are strongly rooted in biology, but the way that they’re expressed and the specific norms in any society are a product of culture. Culture is influenced strongly by biology, and biology is also influenced by culture.

Q. When addressing these issues, some people are afraid that looking for or recognizing differences between the sexes is a way of justifying inequalities.

A. Well, if we find that there is a strong genetic influence on male promiscuity, if that’s true, and I think it is true, then does that mean that it’s okay for men to cheat on their wives? Does that mean that they can never change that behavior? Well, no. But it does mean that there’s a reality there that we have to understand and work with so that we can accommodate the reality of male sexuality instead of denying it, as many, many people do. Many feminists in particular seem to be under that misapprehension, or they’re intentionally misconstruing the evidence in order to try to achieve sex equality.

There are a lot of social problems caused by the differences in sexual appetite between the sexes and what that means for relationships, what that means for society, what that means for happiness and thriving. So, the solution, first of all, is to stop denying the facts, because I think this just causes suffering and makes it harder for us to maximize human thriving. So, first of all, one of the facts that we should be teaching and spreading through journalism and education in the classroom is that just because something exists in nature does not mean that it’s right or good. You know, illness is not good and that’s natural. I don’t think we should have to show that something is natural in order for it to be good. Just because something is innate does not mean that it is destiny or that individuals don’t have any control over their behavior.

Suppose that male aggression, higher rates of physical aggression in males, is due to having a Y chromosome, which ultimately leads to high testosterone, which leads to a higher predisposition for physical aggression. Well, we already know that the environment makes a huge difference. Cultural norms make a huge difference in the extent to which individuals express physical aggression and might get into bar fights or commit murder or rape. We can see that just by looking at different cultural norms in different societies. In some places in the world there’s no strong norms against rape and it’s even encouraged in some places and situations. In others, it is severely punished. So, biology is not destiny.

And if we can recognize those facts about the naturalistic fallacy and the myth of biological destiny, then it makes it easier for us to talk about reality and the changes that we can make socially in terms of policies and laws.

Q. In the book you talk about a fundamental difference between men and women, and between males and females in other mammals. The former continuously produces many small and, to some extent, cheap reproductive cells (sperm), and the latter produces large cells (eggs), which are much scarcer. This means that throughout history the two sexes have had different incentives with respect to their behavior and that has caused tension between the coexistence of the two.

A. If you’re not an evolutionary biologist, it’s difficult to historically appreciate the depth of over a billion years of sexual reproduction, and this has become elaborated and elaborated and elaborated on as behavior. So, when we’re looking at mammals who bear the time and energetic costs of internal fertilization, you know, it’s not like fish or frogs or something. It’s that we not only have internal fertilization, internal gestation, and once we actually expel the offspring to the outside world it’s almost like it’s still in us because we’re still growing it with our bodies, you know, breastfeeding. This is a tremendously impactful imbalance in reproductive investment.

So, the way we live now is weird, just bizarre from an evolutionary point of view. We’re kind of freed from that energetic burden but our psychology hasn’t been completely released from that lifestyle, those needs. Women typically want to have fewer sexual partners for a reason, because each potential conception is a large energetic burden, whereas it isn’t for men. So we still retain these differences in reproductive psychology, and sex hormones and the differences in sex hormones really do condition and promote a lot of these differences.

I don’t know of any culture in which female promiscuity is celebrated and encouraged and male promiscuity is severely punished”

These differences are not just limited to sex and aggression. As it turns out, there are differences in professional interests. Women are more likely to go into helping, nurturing professions, and men are more likely to go into professions that involve more risk and risk-taking. Physical risk-taking is one of these sex differences because it could shorten a man’s life relative to not taking those risks. If taking risks has strong reproductive payoffs, that can outweigh the costs or the risks of dying, basically. So, for men, physical risks have reproductive payoffs, but that’s not necessarily true for females who need to live a long, healthy life to maximize their reproduction.

So yeah, there are these differences. The evidence for hormonal contributions to these differences is not as strong as the evidence of hormonal contributions to sexual behavior and physically aggressive behavior. I think culture does play a strong role there, but it’s hard to know because we have these sex roles where those kinds of differences are reinforced culturally. So we can’t really know how much is biological, how much is cultural. We know that there is a strong interaction there. But my personal view is that striving for equality of outcome – meaning we have equal levels of men and women across different professions – seems totally misguided to me, because I do think there are differences in preferences. And I think what we should strive for is equality of opportunity and equality of pay. It would be great if teaching and caregiving, say, nursing, paid more than they do because these are more female-typical professions. But males are involved in professions that are pretty brutal in terms of their physical demands, and they deserve to be compensated for that too.

Q. But changes in an ecosystem change the biology of the animals that live in it. In an environment where there’s less need for aggression to get ahead or to mate, would testosterone levels also drop?

A. It’s hard to gather really good data [on testosterone, aggression and cultural differences]. Say we compare people in Europe with people in Japan. We know that there are testosterone differences that vary with ethnicity. And that has to do with something called a polymorphism that exists in the gene codes for the testosterone receptor. So there are differences genetically in the testosterone receptor that make it more or less responsive to testosterone. So you can take two guys who have the same level of testosterone. They can be of different ethnicities or not. But if you just look at the length of this CAG repeat in the gene, people who have longer CAG repeats have less active androgen receptors, and people who have shorter repeats have more active androgen receptors. So, for the same amount of testosterone, you could have very different effects individually.

There are studies showing that men in East Africa who live as hunter gatherers, the cultural norm is for [those] men to be very involved with their kids, to have lots of physical interaction in terms of carrying and feeding them, playing with them; fatherhood is really valued. And in those men, testosterone levels are lower, and they go down when the babies come. So, this is something that characterizes fathers everywhere in humans and in only less than 5% of mammals do we see male paternal investment where the fathers actually stick around and help to take care of their offspring. So, this is the case in humans, but it depends, of course, on the environment. And in environments where males do provide for their offspring, the offspring are more likely to survive, and the men’s testosterone tends to decline. That is a product of the culture. That’s because the cultural norm is for men to invest in their offspring. There’s another African group where men do not invest in their offspring, it’s kind of a warrior culture. Those men have babies and are in the same ecological environment, but their behavior is different. They’re not investing in their offspring in terms of actual interaction with them. So, in those men, we do not see a decline in testosterone.

Cultural norms can shift. Testosterone can reduce testosterone. And we do see this consistently in men all over the world who are highly involved with their kids, especially when they’re little. But I cannot really say that we have evidence that any cultural norm has changed a level of aggression. You know, we can attribute a change in testosterone to a reduction in aggression. I’m not sure I could say that it is lower testosterone in any culture that is then also causally related to low aggression and relatively low aggression in that culture. But it could be. I think that could definitely be.

In environments where men take care of their children, the offspring are more likely to survive and men’s testosterone levels tend to drop

Q. In the book you talk about differences between gay and lesbian behavior. Could this have to do with the way men and women are brought up, regardless of whether they are gay or straight, or can it be explained by biological differences to some extent?

A. Homosexual men have way more sex and way more sex partners than lesbians. It’s a fact. It’s a pattern. Everybody knows this is true, it’s totally fine. There’s no, like, moral judgment here. This is an observation. But the reason that gay men are having more sex is because they can. And because of testosterone. We know from studies on people who transition from one sex to another, or from one sex role to another, females who take male levels of testosterone as part of a gender transition report, pretty much across the board, with some variation obviously, but on average, the sense that a female gets when she takes male levels of testosterone is, whoa, this is the way that males go through the world. They start really obsessing about body parts, for one thing. This is somewhat consistent with the literature. So if you look at the scientific literature, it’s clear that sex drive is one of the strongest psychological responses from taking testosterone, that it really cranks up when you go from living as a woman to living as a man and take male-typical levels of testosterone. And I’ve had many conversations now with trans men and trans women, as I did in the book. It’s sort of mind-blowing for a female to start living as a male with high testosterone and to feel how strong the sexual urges are.

Not only does the libido really shoot up, but the nature of sexual attraction changes. And again, this isn’t true for everyone, but many females who transition into living as males also feel this reduction in the requirement for emotional intimacy before sex. And there is that increased attention to the body and an increased attraction to the body as a sexual object, as opposed to the sense that sex and sexual attraction are about a whole human being. So this is something that actually happens: sexual objectification sort of rises with testosterone.

And we see the same thing happen in the other direction when males transition and start living as females: we see a reduction in their sex drive, which many trans women say is a relief. And it’s not that they’re not horny. It’s not that they don’t get pleasure from sex. It’s just that it’s not the same intense drive that it was when their testosterone was high.

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