Review of T(ESTOSTERONE)
Carole Hooven gives the rundown on the role of T across development
Sex-differences, although never completely non-controversial, have had a resurgence of controversy in recent years, especially as discussions of gender identity and sex have come center stage in public discussion. From a behavioral endocrinology lens, Testosterone, or referred to simply as T, is the star of the show.
But why is T so controversial? Well, because it’s what makes men, men. And while women also have T, men’s T levels are 10 to 30 times higher than wonmen’s. Whereas many sex-differences that social scientists study, say personality traits or height, have clear mean average differences, they also have considerable overlap to the point where it’s relatively easy to think of a man you know that is shorter than a woman you know. But T is different. It’s a true bimodal distribution with no overlap among healthy men and women. Now that’s a sex-difference.
In T: The Story of Testosterone, the Hormone that Dominates and Divides Us, Harvard lecturer Carole Hooven dives deep into the T literature to clearly explain what T is and how it makes the difference between men and women across our lives. Although scientists are still learning a lot on the detailed mechanisms, critical periods, and cascading pathways, one thing is clear: T is what makes boys, boys, and men, men.
How so? The short version is that from the earliest weeks in pre-natal development, T goes to work in developing and differentiating humans’ reproductive systems – our internal reproductive organs, such as testes or ovaries, vas deferens or fallopian tubes, or a penis or clitoris. In utero and in the months after birth, T continues is journey to masculinize the brain of males. And later on in late childhood and throughout puberty, T acts to develop secondary sex characteristics, like a deep voice and musculature, in addition to aggressive and sexual behavior.
Put simply, adding T to development sets off a cascade of developmental events that masculinizes the brain and body. Having a Y chromosome with its critical SRY gene and functioning androgen receptors (that process T) is what signals the body to develop as a male. A crucial piece of evidence for how T acts on the body is the case of individuals with Complete Androgen Insensitivity Syndrome, or CAIS. Individuals with CAIS are chromosomally male, with XY chromosomes, but they do not have functioning androgen receptors, which means that no matter how much T their body produces, it cannot be used to “fuel” masculinization across development. These individuals look characteristically female on the outside, and typically identify as female, rather than male, despite having internal male reproductive organs.
Without T, then, human embryos go on to develop as characteristically female, the “default” mode of human development.
Hooven’s T describes the above process in far more expert detail than I’ve provided here, in addition to describing the evidence about T on brain development, aggressive behavior, and sexual behavior.
Finally, and somewhat controversially, Hooven dives into the literature on transgender hormonal therapy and puberty blockers. I tend to not read much about (online and academic) controversies regarding sex-differences and ‘cancel culture’ because I find it boring, but her last chapter, “T is Transition” is presumably what was at the crux of some blow back on Hooven for her book. For what it’s worth, her writing on this topic was utterly uncontroversial from my reading, and I learned more about how puberty blockers function in this context.
Overall, T was an excellent book on the role of testosterone across human development and how it makes males men. Although I knew the higher-level findings, and much about reproductive development, I learned many new details that I plan to use to update some of my own development course lessons.
Published: July 2021
Format: Hardcover
If you think this sounds interesting, bookmark these other great reads:
When Men Behave Badly: The Hidden Roots of Sexual Deception, Harassment, and Assault by David Buss (2021)
Innate: How the Wiring of Our Brains Shapes Who We Are by Kevin Mitchell (2018)
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Good review. I am about halfway through the book. One thing I appreciate about it is that the author names the various books published in the last decade that attempt to minimize or completely discount the role testosterone plays in explaining differences between the sexes. When I read about those books when they were first published, I tried to keep an open mind, however they seemed to fly in the face of both everyday experience/ common sense and my own reading / scientific learning.
In that way, I find this book provides a helpful counterweight to what feels like a popular consensus that testosterone doesn’t explain anything about physical or behavioural differences. It’s also glaringly obvious that those books and that message are motivated by an argument that doesn’t follow from the science: that real physical and behavioural differences between sex, partially explained by our biology, can excuse, in the moral / legal sense, the actions of individuals of either sex.
I guess the interesting question is, given the science (as Carole presents it), what sorts of moral and legal conclusions can or should follow? In some areas we are comfortable excusing behaviour that is ‘caused’ by circumstances beyond our control, in other areas that’s clearly impractical or morally repulsive! But that’s where I see the real action. I think the same goes for discussions around Harden’s book - let’s take the science for what it is, but what follows from it as a matter of policy, legally, morally, etc.