Bitch: On the Female of the Species

by Lucy Cooke

To all the bitches in my life Thank you for the love and inspiration

And as far as evolution was concerned it was males who drove the bus of change. We females could hop on for a ride thanks to shared DNA, as long as we promised to keep nice and quiet.

A sexist mythology has been baked into biology, and it distorts the way we perceive female animals. In the natural world female form and role varies wildly to encompass a fascinating spectrum of anatomies and behaviours. Yes, the doting mother is among them, but so is the jacana bird that abandons her eggs and leaves them to a harem of cuckolded males to raise. Females can be faithful, but only 7 per cent of birds are sexually monogamous, which leaves a lot of philandering females seeking sex with multiple partners.

As ingenious as it is, natural selection cannot account for everything we find in nature. Darwin’s evolutionary theory had some gaping holes in it, caused by elaborate traits like the stag’s antlers or the peacock’s tail. Such extravagances offer no benefit to the general process of being, and could even be considered a hindrance to everyday life. As such they could not have been sculpted by the utilitarian force of natural selection. Darwin recognized this, and for a long time it tortured him. He realized there must be another evolutionary mechanism at play, with a very different agenda. That, Darwin eventually realized, was the quest for sex – and so he named it sexual selection.

Female animals are just as promiscuous, competitive, aggressive, dominant and dynamic as males. They have equal right to drive the bus of change. It’s just that Darwin, along with the coterie of gentlemen zoologists that helped inform his argument, couldn’t, or perhaps wouldn’t, see them that way.

Here was a man that married his first cousin Emma, only after drawing up a list of nuptial pros and cons.

a letter to a friend, has, to Darwin’s shame, been preserved, revealing his most intimate thoughts for all to judge in perpetuity. In just two brief columns – ‘Marry’ and ‘Not Marry’ – Darwin thrashed out his inner connubial turmoil. His chief concerns were that he would miss out on the ‘conversation of clever men at clubs’ and might therefore succumb to ‘fatness and idleness’, or worse, ‘banishment and degradation with indolent idle fool’ (which is perhaps not the way Emma would have chosen to be described by her beloved fiancé).

The anarchy of sex: what is a female?

When a worm pushes through her subway ceiling, she quickly sniffs it out using a long pink snout that can actually smell in stereo – each nostril acts independently, allowing her brain to accurately compute the direction of dinner in the pitch black. Her quarry, once caught, isn’t killed immediately; instead, the mole paralyses it with her venomous saliva so it can be stored alive in a specially constructed larder without turning to rot. As many as four hundred and seventy wrigglers have been recorded in one lucky mole’s pantry, which is helpful as she needs to consume over half her body weight in worms a day.

evolution has equipped the mole with some cunning specializations. Her blood sports a modified form of haemoglobin that increases her affinity for oxygen and tolerance of toxic waste gases. And she sports an extra ‘thumb’. Just like in the panda, a bone from her wrist has shot off on its own evolutionary path and formed a useful new digit for shifting extra earth. But perhaps most impressive of all are the female mole’s balls.

once the job of reproduction is done, this egg-making tissue shrinks and the testicular tissue expands until it is actually larger than the ovarian. The female mole’s testicular tissue is full of Leydig cells that make testosterone, but not sperm.

It does both in the female mole, giving her the evolutionary edge underground: extra digging power and added hostility for defending her pups and worm larder.

The female mole forces us to confront age-old assumptions about what distinguishes the sexes. For the majority of the year, on a genital, gonadal and hormonal level, the mole sow could easily be mistaken for a boar. So, how do we know she’s a female?

Most biologists agree that animals don’t have gender.

When biologists talk about females they are referring only to their sex, but what does that mean?

The earliest life forms simply split, fused, budded bits off or cloned themselves in order to multiply.

Starting at the most superficial level, many would consider genitals an easy indicator of sex. But the female mole’s ‘phallus’ blows that notion clean out of the water. She’s no freak. Dozens of female animals from tiny cave-dwelling barklice1 to giant African elephants, sport ambiguous sexual anatomy that’s commonly described in phallic terms.

Male spider monkeys are the sex with no apparent penis, since they keep theirs tucked away inside. Females on the other hand have a very obvious pendulous clitoris, known in biological circles as a ‘pseudo-penis’. Such androcentric terminology grates somewhat, especially when you consider that the female spider monkey’s ‘fake’ phallus is in fact longer than the male’s ‘real’ phallus.

When a female fossa is born she has a small clitoris and vulva, as might be expected. Then, at around seven months of age, something odd starts to happen. The fossa’s clitoris enlarges, grows an internal bone and acquires spines to become a facsimile of the male’s penis. It even exudes yellow liquid on its underside, like an adult male’s. The female fossa sports her penile clitoris for a year or two, until she becomes reproductively active, when it magically disappears.

Ancient naturalists believed the hyena to be a hermaphrodite on account of the female’s pudenda, which are the most sexually ambiguous of any known mammal’s. Not only does the female spotted hyena have an eight-inch clitoris that’s shaped and positioned exactly like the male’s penis but she also gets erections. Both female and male spotted hyenas display and inspect one another’s sexual tumescence during ‘greeting ceremonies’. Crowning all this female virility is what appears to be a prominent pair of furry testicles.

the female spotted hyena is the only mammal with no external vaginal opening at all. Instead she must urinate, copulate and even give birth through her curious multi-tasking clitoris –

males and females are so similar that they can be differentiated only by ‘palpation of the scrotum’ – something of a last resort, one assumes, when sexing an animal famous for its bone-crunching bite.

Scientists have also been fascinated by her similarly ‘masculinized’ body and behaviour. Females can be up to 10 per cent heavier than males in the wild (20 per cent in captivity). This is unusual, as amongst mammals males are generally larger in size.

Female spotted hyenas are also more aggressive than males. These highly intelligent, social carnivores live in matrilineal clans of up to eighty individuals governed by an alpha female. Males tend to be the sex that disperses from the natal matriline and, as such, the lowest rung of hyena society: submissive outcasts begging for acceptance, food and sex. Females are considered dominant in most situations, engage in rough play and vigorous scent-marking as well as leading the territorial defence – all behaviours more commonly associated with the opposite sex.

But much to everyone’s surprise, the circulating levels of testosterone in adult female spotted hyenas do not rival those in males.

Mammal embryos, whether they’re female or male, all start off with a unisex kit of parts: an assortment of ducts, tubes and proto-gonadal tissue with the potential to develop into either ovaries or testes.

testosterone plays a primary role in driving the fetal gonad towards becoming testes and the subsequent development of male genitalia. Jost discovered that if he removed the male embryonic gonads early in development, the fetus failed to grow a penis and scrotum and developed a vagina and clitoris instead. Removing the developing ovaries of a fetal female, on the other hand, did not obviously impact her sexual development. Oviducts, uterus, cervix and vagina all developed in an apparently automatic fashion without the need of her embryonic ovaries or their hormones to direct them.

Jost established that high concentrations of testosterone in the male fetus, produced by the developing testicular cells, actively pushed an embryo down the path of male sexual development. In contrast, the creation of a female was seen as a passive process – the ‘default’ result of an absence of gonadal testosterone. Jost’s theory slotted in nicely with the widespread notion, popularized by Darwin, that females were generally passive and males active.

It placed male gonads and androgens in the starring role – the saviours of the sexual paradigm and chief architects of all things male.

Thus testosterone became the executive director of sexual dimorphism; responsible for characteristics ranging from the hefty horns on the stag to the bull elephant’s raging musth and the male walrus’s fearsome size and temper.

At a conference in 1969, Jost explained: ‘Becoming a male is a prolonged, uneasy and risky adventure; it is a kind of struggle against inherent trends toward femaleness.’ The masculine journey was seen as a heroic quest worthy of investigation. In contrast, the now-famous French embryologist referred to females simply as the ‘neutral’ or ‘anhormonal’ sex type. Ovaries and oestrogen were considered irrelevant to our story: inert and insignificant.

Females basically ‘just happened’ because we lacked the embryonic balls to be male. This prejudice has been remarkably enduring and damaging. The legacy of the Organizational Concept is an understudied female system and an unyielding binary view of sexual differentiation, as promoted by the all-powerful developmental male-wash of testosterone. But then along came the spotted hyena with her big phallic clitoris to suggest there’s trouble in the paradigm.

when tested, female spotted hyenas revealed rocketing levels of testosterone during their pregnancy. But, with no testes in sight, what could be the source of this ‘male’ hormone, and how does the developing female fetus manage to survive its omnipotence yet still develop a functioning reproductive system? The answers lie in how testosterone is synthesized.

This steroid is converted by the action of enzymes to progesterone, a hormone commonly associated with pregnancy and the precursor to androgens, which are, in turn, the precursors to oestrogens.

‘There’s no such thing as a “male” hormone or a “female” hormone. It’s a common misconception. We all have the same hormones,’ Christine Drea revealed to me over Skype. ‘All that differs between males and females are the relative amounts of enzymes that convert the sex steroids from one to another and the distribution and sensitivity of hormone receptors.’

Drea is part of the team that established the source of the pregnant hyena’s testosterone. It comes from a lesser-known androgen called androstenedione, or A4, that’s actually produced by the pregnant female’s ovaries. This form of androgen is known as a precursor hormone, as it converts to either testosterone or oestrogen following the action of enzymes in the placenta.

‘There’s a growing body of literature suggesting that hormones can have sexually differentiated effects in different animals. It’s all about amount, duration and timing,’ Drea articulated. Drea’s work clearly demonstrates that making a female is far from a ‘passive’ process, and one in which androgens can play an active role.

the female hyena’s sexual development must also be under dynamic genetic control to resist the overpowering effects of an excess of androgens and still create a functional, if eccentric, reproductive system. But how is still much of a mystery.

The idea that any development process could be ‘passive’ is clearly quite ludicrous – ovaries require just as much active assembly as do testes. Yet for fifty years the ‘default’ female system went unstudied. ‘Sexual differentiation isn’t about describing how you get females and males. It’s only about describing how you get males. For decades people were happy not to have an explanation of how you get the female form and just saying, “Well, it’s passive,”’ Drea asserted.

The genetic recipe that actually determines the sexes is, however, positively byzantine in nature and features an ancient cast of surprisingly androgynous genes.

The Y chromosome was eventually discovered lurking in the reproductive organs of a mealworm some fourteen years later, in 1905, by the American Nettie Stevens – a pioneering female geneticist.Stevens recognized its key role in sex determination, but also received little fame for her epic breakthrough. The same chromosome was also discovered, more or less simultaneously, by a male scientist called Edmund Wilson, who sucked up most of the fame.

Compared to the X, the Y is essentially a runt of a chromosome: stunted and with significantly less genetic material. When it comes to chromosomes, however, it’s not size that matters, it’s what you code with it. And the Y is indeed home to a very significant sex-determining gene called SRY (standing for Sex- determining Region of the Y). In the 1980s Peter Goodfellow’s lab in London finally unmasked this unassuming piece of genetic code as the elusive testis-determining factor in humans.

their triumph at solving the puzzle of sex was, in fact, short-lived. ‘We thought it was going to be the Holy Grail,’ she confessed over Zoom from her home in Melbourne. ‘When my student found the SRY gene we thought it would all be really simple. A kind of switch. But sex determination turns out to be much more complicated than we thought.’

evolution has done nothing to make the work of geneticists easy. The entire process of sex organ determination involves an orchestra of around sixty genes working in concert. These sex-determining genes don’t all exist on the sex chromosomes, let alone sit in a disciplined and gendered fashion on either the X or the Y. They are, in reality, scattered haphazardly throughout the genome. SRY is like their conductor.

Aside from SRY, this orchestra of sixty sex-determining genes is basically the same in males and females. These genes have the ability to create either ovaries or testes, but exactly which gonad they actually produce depends on a complex network of inter-gene negotiation.

This interconnected chaos of androgynous genes explains the plasticity of sex. Subtle tweaks in the expression of any of the interwoven cogs will produce novel variations – the grit that drives evolution forward and allows animals to adapt and exploit challenging new environments.

SRY, the genetic trigger for this orchestra of sixty sex-determination genes, is not the universal master switch for sex across the animal kingdom, or even amongst all mammals for that matter. Enter the platypus. This egg-laying mammal from Australia specializes in being contrary, and its sex chromosomes are no different.

the platypus has five pairs of sex chromosomes. Females are XXXXXXXXXX and males XXXXXYYYYY. Despite this extravagance of Y chromosomes there is no sign of the SRY master switch on any of them.

The platypus is an ancient mammal whose group, the monotremes, diverged from humans some 166 million years ago. Its quirky sex chromosomes provided Graves with valuable insights into the evoluti...

‘SRY is just one way of kicking off the pathway, but you can do it by really almost any one of these sex-determining genes,’ Graves explained, blowing my mind just a little bit more. ‘That is the weirdest thing about sex. There are so many ways of doing it and they look to be quite different, but they’re actually not. They all have to do with this pathway of sixty genes. So, the pathways are similar. But it’s a completely different trigger.’ The platypus genome also revealed something else to Graves: the Y chromosome is losing genetic material.