In our third and final blog post sharing information on men and sex differences from Carole Hooven’s book T: The Story of Testosterone, the Hormone that Dominates and Divides Us, we offer additional facts from the book that didn’t make it into our earlier two articles:
- 20 Facts About Testosterone To BOOST Your Understanding of Men and Boys
- 10 False Claims about Testosterone and Sex Differences Refuted by Harvard’s Carole Hooven
For example, did you know that the changes in a man’s testosterone levels in response to becoming a dad depend heavily on the amount of time he interacts with his children? Learn more below.
Note: Is this author credible?
Given that many intelligent people disagree about matters of sex and gender, we compiled a collection of passages from the book that underpin our confidence in Professor Carole Hooven’s credibility and her book’s truthfulness.
Men’s hormones after becoming a dad
A man’s hormonal response to becoming a father depends heavily on his culture and the amount of time he interacts with his children. For example, dads in the Hadza foragers of Tanzania (who are generally socially monogamous) frequently hold, feed, and play with their babies, while dads in the neighboring Datoga pastoralists (who practice polygyny) are more likely to leave this to the moms and other caregivers. You can guess which dads have the lowest T levels—the Hadza. The T levels of the Hadza dads were found to be almost 50 percent lower than their childless fellows, while the T levels of the Datoga dads were no different from Datoga men without kids.
Physically interacting with young children, doing things like feeding, playing, carrying, or changing diapers, is associated with a T drop in dads. And in many situations, a dad’s focus on his family will increase his overall reproductive success. (p. 198)
Putting one’s life on the line
Since 1904, in the United States and Canada, about ten thousand people have been awarded the Carnegie Hero Medal, which goes to a civilian “who voluntarily risks his or her own life, knowingly, to an extraordinary degree while saving or attempting to save the life of another person.”
About 90% have gone to men. (p. 242)
Men’s violence
Across distant times and places men murder and physically and sexually assault vastly more than women do. Men commit about 90 to 95 percent of all murders worldwide, and they most often kill other men. (p. 163)
Among the hunter-gatherer populations remaining today, the sex differences in homicide rates are comparable to those in the rest of the world: men commit almost all murders, mostly against other men. (p. 165)
Women’s aggression
If you define aggression broadly, so that it includes indirect, maternal, and intimate forms, you can make a pretty good case that human females can be as aggressive as males. And there is clear evidence that women are just as disposed to anger as men. But if you define aggression more narrowly, as the kind of aggression that puts the perpetrator at physical risk, like inflicting bodily damage through acts such as headbutting, rape, and murder, there’s no contest. Men win, hands down. (p. 161)
Who kids play with
Before the age of about two or three years old, kids toddle around with little attention to gender. But for most kids, as soon as they come to understand that they are a boy or girl, in diverse cultures all over the world, they begin to gravitate toward their own kind. The overwhelming majority of children’s playmates are members of their own sex, and this gender segregation peaks around the ages of eight to eleven. Younger kids appear to be drawn to the sex that is playing in a way that they find appealing, leading to fairly loose patterns of segregation. But as kids develop, playing with one’s own sex, no matter what they are doing, becomes more important. (p. 94)
Exposure to high levels of testosterone, even before we are born, masculinizes not only our bodies but also our interests, preferences, and behaviors. (p. 97)
What testicles do
Castration has been common practice across cultures and ages, whether to punish enemies or rapists, prevent the “mentally unfit” from having children, retain the high-pitched voice of a prepubertal boy, embody the identity of a woman, or to create a less lustful servant. (p. 29)
With few exceptions, throughout the long reach of history, the ultimate purpose of removing the testicles of men (and other male animals) has been to deprive them of some of their most quintessentially masculine features, such as physical strength, a deep voice, strong libido, or aggressive tendencies. (pp. 33-34)
Eunuchs were a feature of both ancient Greece and Rome. But there is probably no other culture with a longer, richer history of eunuchs than Imperial China. (p. 31)
In the absence of modern pharmaceutical treatments, typical male behavior and appearance depend on having testicles. As we’ve seen, humans have long observed that without testes, male animals fail to develop (or lose) masculine physical traits and processes like the production of sperm, and (depending on the animal) bright feathers, large, pointy antlers, a long larynx, or big upper-body muscles. And the testes’ influence extends to masculine behavior, like getting an erection, using physical aggression, and being motivated to compete for female sexual attention. (p. 48-49)
The testosterone gap
Testosterone levels in healthy men and women do not come close to overlapping: men’s are 10–20 times those of women’s. In puberty, the gap in T level is even wider—pubertal boys have about thirty times as much testosterone as girls. (p. 246)
If we want to understand what it means to be a male human, and the ways in which boys and men are different from girls and women, we need to understand T. (p. 34)
Circulating testosterone in adults has a strikingly non-overlapping bimodal distribution with wide and complete separation between men and women. (p. 113)
The height gap
In the United States, men are on average 5.5 inches taller than women. (p. 11)
We’d all be female
All humans are very much alike. Still, looking at humanity as a whole, humans come in two visibly distinct forms: male and female. This is due to a small genetic difference: the SRY gene, found on the Y chromosome. Without that gene, the body almost always develops as female. (p. 245)
Planning for reproduction
In many male animals, including seasonal breeders (like the red deer) and nonseasonal breeders (like chimpanzees), dominance relationships are established and renegotiated when no fertile females are present. These relationships affect the resources males can acquire, like territory, that will later affect their ability to find mates. In other words, aggression pays off even when mates are not directly at stake. Changes in T can help males make arrangements for their reproductive futures. (p. 143)
The primary evolutionary function of testosterone is to coordinate a male’s body and behavior in the service of reproduction. (p. 245)
Fecundity
In theory, men’s reproductive success is limited only by the number of one-night stands they can get—and have the stamina for. But the evidence suggests that the most successful men in most hunter-gatherer societies sire only around twenty-five children (a figure that is not completely out of reach for exceptionally fertile women). (p. 190)
Sexual fantasizing
Men tend to fantasize more about sex with strangers and multiple partners, while women tend to fantasize about current partners or people they know. (p. 196)
Women’s libido
Doctors frequently prescribe testosterone “off-label” (i.e., not approved by the U.S. Food and Drug Administration) to women who seek to increase their libido. However, there’s little reason to think it works. (And men may also be overprescribed testosterone for declining libido; as in women, the causes of low libido are complex.) (p. 199)
Testosterone’s effect on the voice
T’s actions on the vocal folds can’t be undone by blocking T or taking estrogen later in life. Once thickened and elongated, the only way to bring them back to their previous state is vocal cord surgery. But the path to a manly-sounding voice is relatively smooth for female-to-male transgender people, no matter the age at which they start their hormonal transition. The voice will begin to drop within two to five months of starting male levels of T and will stabilize within a year. But it may never reach the same depth as that of a natal male. (p. 219)
The Adam’s apple
The Adam’s apple is the most visible evidence of one part of the larynx—the thyroid cartilage—that sits protectively over the vocal folds…The male larynx grows in response to high T during puberty, and the angle at which the two cartilages join is much sharper in men, due to the protrusion of the long (relative to women) vocal folds that the cartilage covers. In men, the two plates of cartilage join at an angle of about 90 degrees; in women, it’s about 120 degrees. The larger larynx and pointy cartilage over the vocal folds both cause the Adam’s apple to protrude more in people who have gone through a high-T puberty than those who have not. The Adam’s apple may grow somewhat under the influence of T in FtM transitions that take place after puberty, but the effect is variable. (p. 221)
Cross-sex hormones
Puberty blockers are (largely) temporary and reversible interventions. The same cannot be said of cross-sex hormones, especially testosterone. When someone decides to hormonally transition, no matter their age, they are signing up for a lifetime of medical dependence on hormones (in addition to undergoing any gender surgeries they may choose, some of which are quite involved). The decision to experience a kind of cross-sex puberty carries more lifelong, serious consequences than the decision to take puberty blockers. But around 95 percent of gender-dysphoric children who use puberty blockers go on to hormonally transition. (p. 228)
Trans people provide evidence that T is a crucial part of the explanation of male sexual behavior; it is not simply the product of upbringing or sexual standards prevailing in the culture. (p. 238)
The penile plethysmograph
The penile plethysmograph is a scientific instrument that allows sex researchers to obtain objective measures of men’s arousal levels. It is a ring that is strapped onto a man’s member that registers changes in its circumference as he watches nature documentaries or pornography, or listens to erotic recordings or classical music. (p. 195-196)
Female hyenas
The female spotted hyena is highly aggressive and gives even seasoned experts difficulty trying to tell her apart from the male. Her clitoris — through which she pees, has sex, and gives birth — looks exactly like a penis. She even has a convincing-looking fake scrotum. (p. 146)
T affects social interactions
T affects relationships and the social environment. For example, mother rats lick and groom their babies to regulate their temperatures and stimulate defecation. The amount of T in the babies’ circulation affects how much mom licks and grooms them! Mom licks and grooms the ones with the highest T levels most. The sons with lower T levels, and the girls, get the least. And the mom’s differential treatment of her kids, in turn, affects the sexual behavior of the adults they become. For example, the males who were licked and groomed the least end up taking longer to ejaculate when they grow up, and they need a longer recovery period before they can ejaculate again. The vital lesson here is that hormones can sometimes affect behavior indirectly, by affecting social interactions, which can change behavior in turn. (p. 88)
See our other two articles based on Carole Hooven’s book about testosterone: 20 Facts About Testosterone To BOOST Your Understanding of Men and Boys & 10 False Claims about Testosterone and Sex Differences Refuted by Harvard’s Carole Hooven