Testosterone Rex by Cordelia Fine

Men take more risks than women, are more competitive, and have a greater drive for both sex and dominance.  Women are more nurturing, take fewer risks, and value fidelity over sexual novelty.  These differences are rooted in human biology.  Over thousands of generations women bore and raised children while men hunted, leading to the evolution of fundamental differences between the sexes.  We see similar differences in a wide variety of other species.  In general males compete for females, while females bear and raise young.  Testosterone is the primary mechanism that drives these sex differences.  When we see a young man in a hot car, aggressive stock traders, or risk-taking sky divers, we're seeing testosterone at work.

You are familiar with this story.  It is simple and is widely understood.  It has only a single flaw:  it's not supported by the modern science of sex difference.

Take for example the concept of 'risk-taking'.   Who is more likely to take risks?  The answer turns out not to be simple.  What kind of risk you are talking about?  A physical risk?  A financial risk? A social risk?  What are the circumstances under which you are asking the test subject to take the risk?  Who is being asked to take the risk and what is their background?  Are we asking a Chinese woman who is a part of a social group of her peers to gamble a trivial amount, a man to take the social risk of disagreeing with his friends on a matter of principle, or a young woman to decide whether or not to have a baby?  (As it turns out,  if you look at mortality rates per 100,000, in the US you are 20 times more likely to die as a result of a pregnancy than as a result of skydiving).

When you look at the research, who takes which risks depends critically on who is being asked, the particular risk under consideration,  and the circumstances under which the risk is presented.  And, in the end, there is no such thing as a generic 'risk-taker'.  Day traders are no more likely than average to enjoy wing-suit base jumping.  In short, the biological sex of the test subject is not the defining criteria that determines what their risk-taking behaviour will be like, not even when you consider the highly gendered lens through which 'risk' has historically been defined for the purposes of social science research.

Testosterone Rex doesn't deny that there are differences between men and women, or deny that evolution has played a role in human biology.  That would be silly, even if Fine does wish that she had the nerve to claim "Testicles are a social construct" just to see people's reactions.  (Not to mention that it would give her an excuse to discuss a species of fish whose testicular development does in fact depend on the individual fish's social status.) 

Instead in this book Fine surveys the state of research on sex difference and dissects the mythology of testosterone. She argues that there is no such thing as biology unaffected by culture, especially for the human species. She also speculates that perhaps the very lack of fundamental behavioural differences between women and men found by modern research is how evolution has manifested itself in humans: after all, our flexibility to adapt to wildly varying circumstances is the basis of our success as a species.  Large and hard-wired differences between the sexes would leave us less adaptive.

Testosterone Rex won the 2017 Royal Society prize for popular science books.  It's easy to see why:  the book is comprehensive, rigorous, relevant, and entertaining.    Nevertheless, I didn't find a copy in stock at a book store until I hit New York City in January.  I hope the book gets the audience that it deserves.