Testosterone Rex by Cordelia Fine

Sayani Sarkar
The Omnivore Scientist
4 min readFeb 19


Testosterone Rex
Unmaking the Myths of Our Gendered Minds
Cordelia Fine
ISBN: 9781785781629
Price: 7.99 GBP
Pages: 256
Publication Date: 02/03/2017

The behavioral endocrinologist Richard Francis coined the term “Testosterone Rex”, a jibe at testosterone’s mistaken ability to be the “super-actor” of sexual selection. A one-stop solution for all social outcomes.

Cordelia Fine takes a witty and entertaining take on the gender bias and sexual difference debate. Comparison with Angela Saini’s Inferior was rife when this book was published. But Fine’s book is largely based on numerous examples from the animal kingdom regarding research in endocrinology, behavior science, and developmental biology. A lot of zoology resides in this book.

Robert Sapolsky, the creator of the behemoth that is Behave (one of my favorite books and a complete fan of his entertaining Stanford lecture series), writes that “A dozen or so millennia ago, an adventurous soul managed to lop off a surly bull’s testicles and thus invented behavioral endocrinology.” Thus began the science to declare that testosterone dictated the whole spectrum of behavior attributed to human males. But do castration experiments deduce that testosterone dictates the dinosaur views about male aggression, competition, ferocious hunt for resources, and sexual promiscuity? No. Several examples from the animal kingdom show that social events (e.g., putting a small territorial fish with large territorial fish in a tank and seeing a reduction in testes size and gonadal activity) regulate gonadal events. Again, the difficulty lies in assuming parity between fish and humans. But controlled behavior experiments also produce results reflecting the same idea. The latter half of the book is repetitive in its treatment of this subject. Several examples that break the stereotype of the Rex start getting similar by the time you reach the end.

My reservation, albeit small, concerns the statement that hormones do not affect behavior as stereotyped in our society. This negates a lot of anecdotal data that remain unaccounted for. Especially, where female individuals are disregarded by practitioners and clinicians regarding their changing bodies or behavior across their lifetimes. Sexual dimorphism has evolved for different roles. A train of thought that aims at equity also can be complacent regarding diagnoses of conditions in female biology that stem from hormonal differences. This remains a sore point for me that reflects in the slow research in female biology to this date.

Promiscuity has largely been attributed to be a male-dominated area. But as the writer points out, the animal kingdom is rife with examples where females (humpback whales and fruit flies) are sexually promiscuous. Possible reasons like genetic benefits, healthier offspring, and weeding out weaker specimens by creating sperm competition have been proposed for female promiscuity. The results are logical when seen in the context of the environment a particular insect or fish lives. Some of these examples also show males discriminating while copulation to save either sperm quantities or conserve energy in mating strategies. Faunal Valentine’s day preparations are harder for some species. Just going with Fine’s humor in the book. Certain passages are simply laugh-out-loud material. Snarky and hilarious. For example,

The males of some species (like the stinkbug and the bucktooth parrot fish) address the problem of sperm expenses in a Scrooge-like manner, grudgingly “tailor[ing] the size of their ejaculates” to the reproductive quality of the receiving female.

A weird chapter talks about sex differences that lead to financial decision-making capabilities. These studies have the usual caveat of being conducted largely in the Western nations and leaving the Global South behind. I witnessed a similar thread couple of months ago when I read a book on the neuroscience of navigation. Women in Egypt and Saudi are behind Scandinavian countries as far as navigational talents in driving are concerned. This ultimately leaves behind the prerequisite of the awareness required for driving (I don’t own a car, can’t drive, and won’t drive because of my carbon footprint) or in this book’s context, the ability to invest in fluid markets. Differences in making financial decisions and mathematical abilities are largely due to cultural and social differences.

Nonetheless, as Fine writes, this doesn’t mean the brain is asexual. Several sex differences have been identified throughout the human nervous system, but only a few are linked to differences in behavior. Genetic, hormonal, and gonadal differences affect brain development and function but individual human behavior is a much more complex and plastic product of a large number of factors other than the ones mentioned above. Environment, epigenetics, genetic, hormonal, and gonadal. Biological sex is a cocktail much more complicated than controlled experiments.

Ultimately, mating patterns and rearing habits are diverse across the animal kingdom. So, why should sexual stereotypes reign in the public imagination? But Testosterone Rex celebrates the said diversity and not the sociopolitical landscape of patriarchial gaze regarding gender inequality. For that, Angela Saini’s Inferior is a superb read.