One memorable evening, I mentioned over the family dinner that it was time to get our newly acquired dog de-sexed. At this point I should explain that my older son has a strange, unchild-like interest in taxidermy. Thus, ever since this boisterous, loving canine entered the household, my son has been campaigning for the dog, after it dies, to live on not just in our hearts, but in a tasteful, formaldehyde-preserved pose in the living-room. To my son, then, my remark about neutering offered the possibility of a stopgap until that day should come. Dropping his cutlery in excitement, he exclaimed, “We could have his testicles made into a key-ring!”


A lively debate on the merits of this idea then ensued.

I share with you this intimate moment from Fine family life for two reasons. First, I wish to draw attention to the fact that – contrary to a prevailing view of the feminist as the kind of person who could think of no better way to start a workday than to unlock her office with a set of keys from which dangles a man-sized pair of testicles – I strongly vetoed my son’s suggestion.

The second reason is that there is a useful metaphor here. A pair of testicles hanging on a key-ring is bound to capture attention; to mesmerize. “That’s some key ring you have there,” people might politely comment. But what they would really mean is that in some important way your identity has been defined. Who you are is someone with a testicle key ring.

Biological sex can capture our attention in much the same way. We are spellbound by it; keep it constantly in the spotlight. And we often think of biological sex as a fundamental force in development that creates not just two kinds of reproductive system, but two kinds of people.

At the core of this way of thinking is a familiar evolutionary story. As we all know, the two parents of every human baby are owed grossly unequal debts for the miracle of life. According to my rough calculations, the mother is due more or less a lifetime of unwavering gratitude in return for the donation of a nice plump egg, forty weeks or so full bed and board in utero, many hours of labour, and several months of breast-feeding. But for the father, who by the time of birth may have supplied nothing more than a single sperm, a quick appreciative nod might well seem sufficient. This fundamental sex difference in biological investment in a baby means that, at least in some respects, in our ancestral past the sexes required different approaches to life to achieve reproductive success. And so, the various versions of this well-known account continue, men evolved a promiscuous streak, and to be risk-taking and competitive, since these were the qualities that best enabled them to accrue the material and social resources attractive to women, and to turn that sexual interest into a reproductive return. But the ancestral women who most often passed on their genes were the ones psychologically inclined to play a safer game, more focused on tending to their precious offspring than diverting their energy toward chasing multiple lovers, riches and glory.

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All of this appears to be cool, dispassionate, unarguable evolutionary logic. Feminists can rail at the patriarchy and angrily shake their testicle key chains all they like: it’s not going to change the fundamental facts of reproduction. Nor will it change the cascade of consequences this has for the brains and behaviour of modern-day humans. These effects, we’re often told, apparently encompass activities well beyond our ancestors’ wildest imaginings, like science, Formula 1 racing or investment banking.

We certainly often behave and talk as if the sexes are categorically different; Men Are from Mars, Women Are from Venus. In toy stores, sex-segregated product aisles (real or virtual) assume that a child’s biological sex is a good guide to what kinds of toys will interest them, or in the workplace, many consultants take it for granted that biological sex provides a useful proxy for the skill-sets employees bring to organizations.

When we think of men and women in this complementary way, it’s intuitive to look for a single, powerful cause that creates this divide between the sexes. And if you’re thinking right now of a hormone beginning with the letter T, you’re not alone. The subtitle of a recent book on testosterone, “Sex, power and the will to win,” captures exactly those masculine qualities that, according to received wisdom regarding our evolutionary past, were so necessary for male reproductive success. As the hormonal essence of masculinity, testosterone would ensure that the desire for sex, the drive for power, and the will to win develop far more strongly in the sex for whom it was reproductively beneficial in our evolutionary past.

This is Testosterone Rex: that familiar, plausible, pervasive, and powerful story of sex and society. Weaving together interlinked claims about evolution, brains, hormones, and behaviour, it offers a neat and compelling account of our society’s persistent and seemingly intractable sex inequalities. Whenever we discuss the worthy topic of sex inequalities and what to do about them, it is the giant elephant testicle in the room. What about our evolved differences, the dissimilarities between the male brain and the female brain? What about all that male testosterone?

But dig a little deeper and you will find that rejecting the Testosterone Rex view doesn’t require denial of evolution, difference, or biology. Indeed, taking them into account is the basis of the rejection.

Take the familiar evolutionary story of sex differences. There is no dispute that natural selection shaped our brains as well as our bodies. But decades of research in evolutionary biology have destabilized the key tenets once thought to apply universally across the animal kingdom, whereby arduous, low-investing males compete for coy, caring, high-investing females. The sexual natural order turns out to be surprisingly diverse, and we also bring our own uniquely human characteristics to the sexual selection story. For many years now, science has been rewriting and humanizing this evolutionary account.

For instance, female promiscuity is abundant across the animal kingdom – from fruitflies to humpback whales – and widespread among primates. As an example of how scientific understanding is changing, observations over two years of the buff-breasted sandpiper, a beautiful shore bird, suggested that, in line with traditional expectations, one single, fortunate male was involved in 80 per cent of matings in the first year, and all of them in the second. In other words, other males seemed to barely get a look in. But paternity testing of over 160 offspring hatched during that time revealed that much had taken place out of sight. Far from one or two males having all the reproductive luck, at least 59 different males had fertilised eggs in the 47 broods tested! (Eggs from the same brood can have different fathers). Recall, there’s supposed to be only one father shared around, instead “there were more fathers than mothers”. It’s as if the women of a harem were to casually comment to the sultan: “Oh no, that child’s not one of yours – that’s the second footman’s daughter… Eh? Ah, sorry. He’s not yours either, that’s the son of the chauffeur. Hang on, sultan, we’ll find your kid. Nadia… Nadia! Do you remember which of these kids is the sultan’s? Oh yes, that’s right. That boy over there playing with his half-brother. He’s yours. Almost certainly.”

Moreover, as evolutionary ecologist Sarah Blaffer Hrdy pointed out in the 1960s and 70s, a female’s status and situation can have major repercussions for her reproductive success. Dominant female mammals have been found to get more and higher-quality food, better access to water or nest sites, and to enjoy reduced predation risks. Given everything it takes to gestate, lactate, and successfully see off one’s young into the world – food, protection, maybe a nice little nest or privileged use of a feeding ground – this makes sense. Those better able to compete for material and social resources will be more likely to successfully pass on their genes to the next generation.

In short, neither promiscuity nor competition are necessarily the preserve of male reproductive success.

Contrary to the notion of men diverting their energy toward chasing multiple lovers, there is evidence to show males can be choosy too. Thinking of sex as a throwaway act for males – at the rock-bottom price of a single sperm from a limitless supply – is profoundly misleading. As a number of scientists have pointed out, males do not offer up a single sperm in exchange for an egg; instead, they produce millions of sperm at a time (in humans, on the order of two hundred million). “The notion that males can produce virtually unlimited numbers of sperm at little cost is antiquated and demonstrably incorrect”, one review concludes. Indeed, in one spider species, males run out of sperm after mating just once. 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. Others, like the marsupial mouse Antechinus, take the opposite approach of splurging abandon, essentially mating to death during a brief breeding frenzy. In Mark Elgar’s evolutionary biology lab at the University of Melbourne, male stick insects are offered a mating opportunity every week. Despite apparently having nothing more demanding to do all day than resemble a stick, they only rouse themselves to take up this mating opportunity 30-40 per cent of the time.

The point here is not that humans are really like buff-breasted sandpipers or stick insects, but rather that there is incredible diversity of sex roles across the animal kingdom: across species, biological sex is defined by gamete size but this, in turn, doesn’t determine reproductive arrangements and roles. In fact, even within a species, sex roles can be remarkably dynamic. Female bush crickets, for instance, are fiercely competitive when food resources are low, presumably because males supply them with nutrient-rich sperm packages. However, when the environment is abundant with the pollen they feast on, they switch to a more “conventional” choosy approach. Even when it comes to something as fundamental as mating, then, the effects of sex are more open-ended and flexible than we might tend to assume.

No doubt Testosterone Rex will – like a taxidermied family dog that persists past its natural life span – continue to linger on in the public and scientific imagination. But it is extinct. It misrepresents our past, present, and future; it misdirects scientific research; and it reinforces an unequal status quo. It’s time to say good-bye, and move on.

The winner of the 2017 Royal Society Insight Investment Science Book Prize will be revealed on 19 September.

Testosterone Rex by Cordelia fine is available now (£11.99, Icon Books)
Testosterone Rex by Cordelia fine is available now (£11.99, Icon Books)


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