Women After All: Sex, Evolution, and the End of Male Supremacy (13 page)

The long promoter was much more common in the wild East African chimps than in either captive center, where the chimps descended from West African forebears. In the males in the Louisiana population, the long promoter was associated with “smart” social
behavior, such as forming coalitions and initiating play, as well as with friendliness; this does not seem to fit with the Yerkes finding of more stable personalities and less dominance in males with the short version, but the behavioral measures were very different. The needed behavioral analyses of the wild chimps have yet to be done.

However, all the studies so far point to the importance of the vasopressin promoter as a basis for variation in social behavior. And most remarkably of all, research in Sweden by Hasse Walum and his colleagues has shown that natural variation in the promoter (although not the same as the variants in voles) is linked with partner loyalty in humans.

Sometimes after an expert delivers a lecture on this research, a young woman will come up and ask, half-jokingly, for something she can put in her boyfriend’s beer to make him commit. There is no such thing now, because we can’t insert genes through beer; if your boyfriend uses snuff or an inhaler, you could theoretically add oxytocin, which seems to make people of both sexes more trusting and affectionate. (Don’t try this at home.) But the question of whether we as a species could evolve a more perfect marital union, with more loyal males who are better fathers, is something else again. As we will see, we may well be in the midst of such an evolutionary change right now. And who knows: perhaps the next generation of scientists will find a way to speed up the change by spiking beer.

Chapter 4

♦

Primate Possibilities

N
ow we come closer to our own corner of the biological world and look at the roles of males and females in our cousins, the primates. In the evolutionary time scale we began as primates called prosimians, and so they have much to teach us about where we have been and where we are going. And they have news for us about male supremacy.

Lemurs, the most common prosimians, dwell—or, rather, move restlessly—in the lush forests of the large island of Madagascar, off the east coast of southern Africa. They are less like us than monkeys and apes but more like us than any other mammals. Once found throughout the world, they were beaten back by the monkeys their ancestors gave rise to—except in their island world, which monkeys never inhabited. They represent roughly the kinds of animals we were before we became monkeys or apes, and that’s a big part of their interest.

But there is also this: in all lemur species, females dominate males. This happens in the wild and in captivity, in one-on-one fights over food, turf, and elbow room, in subtle and crude ways.
As Alison Jolly—the great pioneer of lemur field studies who died in 2014—put it, lemur life is one long soap opera. The males have nasty fights among themselves—over females, for instance—and females compete with one another as well. In some but not all species, females are larger. But the key fact is, females dominate, while cowed, submissive males know and keep their place. Females can dominate one-on-one, but they usually do it through female coalitions as well. This is called the
lemur syndrome,
and it may be a key to the evolution of primate social intelligence
.

Take the blue-eyed black lemurs, stunningly beautiful animals with striking eyes, from pale azure to a shocking electric blue, set in plush black fur. As they meander through the trees, balancing on the branches using their long, lithe, bushy tails, they might almost seem like large, elegant cats, but their eyes are deeply intelligent and their hands look and work like ours. In a study by primatologists Leslie Digby and Alexandra McLean Stevens, blue-eyed black lemur females won 99 percent of contests with males, combining social coercion—threats and subtler messages—with more frequent outright aggression. Growing up, the boys did win a few contests, but girls still ruled and got better at it as they became unbeatable adults. Despite their submissiveness, some males manage to mate with multiple females, which means that there is serious female choice.

Yet varied lemur mating patterns all seem to work in the female’s favor. Brigitte Marolf and her colleagues compared the red-bellied lemur, which is monogamous, to the crowned lemur, where both sexes mate multiply. Crowned males were more aggressive with each other, but females were also tougher on them, and they dutifully groomed females more than did their faithful red-bellied counterparts. Nevertheless, despite these differences, males in both species bowed to female power.

This is also true in ring-tailed lemurs—gray creatures with striking black bands circling their long, thick tails—who live a highly social life. They like to huddle and sunbathe, bellies angled skyward,
which makes them seem mellow, but every female dominates every male, despite the fact that the males are just as big. They also have similar androgen levels, although females double their levels during breeding season—along with their belligerence. Psychologist Christine Drea and anatomist Anne Weil showed in 2008 that (like hyenas) ring-tailed females have naturally male-like private parts; from a distance these organs could be a penis and testicles, and when measured up close they have the anatomy of female primates given male hormones. Their ultimate ornament is an enlarged, dangling clitoris—as in humans, the only organ that has no known function except pleasure, but in the lemurs it is much larger. So ring-tailed females are not just lording it over males but also probably thoroughly enjoying it.

Yet in the end, the cat’s meow of female satisfaction may occur in the minute gray mouse lemur. Both sexes are wide-eyed cuties, Yoda dolls straight out of a
Star Wars
collection, but like teacup Chihuahua puppies, they will fit in the palm of your hand. Yet these females too have no trouble lording—ladying?—it over the pliable males in their nocturnal world. One research paper, titled “Sex in the Dark,” showed that males must travel widely to reach their hearts’ desire, but with females calling the shots, most litters have multiple fathers. In another study, published in 2012, ecologist Doris Gomez and her colleagues found that females prefer males who defeat other males, despite the fact that those same winners can’t beat
them.
Picture perhaps an athletic princess who watches her suitors wrestle it out (knowing she could pin the best of them) and then deigns to let the winner do her bidding—on her terms.

In a 2012 laboratory study, behavioral ecologist Elise Huchard and her colleagues controlled the size of the sexes. She predicted that smaller females would mate with more males—“convenience polyandry,” it’s called—since they’d be less physically capable of resisting the boys’ advances. Wrong. The larger the female, the more mates; the researchers called this “adaptive polyandry,”
because those females give the nod to one after another—the wrestling matches just decide who’s first in line. The paper drily noted, “Mouse lemur females exert tight control over mating and actively seek multiple mates, suggesting that polyandry might constitute a more rewarding strategy” than the usual pattern of female choice
before
mating. Rewarding, perhaps, in more ways than one.

The great primatologist and evolutionary anthropologist Sarah Blaffer Hrdy gave us glimpses of all this decades ago, in a book intriguingly called
The Woman That Never Evolved
. That nonexistent female was the passive one of male myth, a sex object mysteriously both cool and hot, out of reach and responsive, virgin and courtesan, with nary a tough bone in her body or an aggressive thought in her head, who magically morphed into an all-giving earth mother as soon as you—you clever boy—figured out how to bring her down off her pedestal. This myth had an evolutionary version, in which female primates stood by while males fought over them, winner take all. What could the poor delicate things do, anyway? They made the best of it. After all, didn’t they just want the best fighters to protect them, the best hunters to feed them and their babies, the boldest, toughest sires for their sons?

The myth ran deep in our culture. It was Achilles and Agamemnon fighting over the beautiful slave Briseis; Greece and Troy spilling rivers of blood over lovely Helen; Odysseus, after countless exploits and no few dalliances, come home to find Penelope, after twenty years, loyal as ever, warm, waiting, having rebuffed his every rival. And if you think the Judeo-Christian tradition is different, read Genesis or Judges. In these sacred sagas, men fight, while with few exceptions women wait and take what they can get. At best, women have wiles, only rarely pluck or strength. But these, we will see, were accounts of a very different type of culture than the one we evolved in. And women, in all likelihood, did not write those books. The woman that
did
evolve was a different one.

Hrdy knew this because she was a courageous field primatologist who braved many difficulties to do a landmark study of langurs—large, sleek, grayish-tan monkeys of central India. She made famous a phenomenon that intellectually tacked down one end of a continuum of extreme male violence: competitive infanticide. Others would find it in many other species—over fifty at last count among primates alone. But her langurs were a stunning first revelation. In a nutshell: Their troops had unstable male hierarchies. Females, their relatives, and their young formed the core, but the males would, after a couple of years in power, be driven out by other males. When this happened, the new males killed all infants under six months of age, which made their victims’ mothers sexually acquiescent again—this time, to them.

At first glance, it seemed the old story of pure and rather vicious male privilege. Females had to watch their infants bitten and torn and, in due course, had to mate with their tormentors, much as the women taken in slavery in countless wars became wives and concubines of their enemies. But, in fact, it was not so simple. Mothers fought back. Langur females valiantly tried to prevent the new, empowered males from getting to their babies and risked their own lives trying to protect them, holding on or grabbing them back even after the infants were gravely wounded. And they helped each other, deploying alliances of sisters, mothers, and female cousins, sharing the risk and cost of joint resistance. If they succumbed in the end to overwhelming force, it was not without a fight.

The old Western myth was wrong in many other ways, too. Female primates were never passive in any situation. Even in ordinary times, when they weren’t facing anything as intense as infanticide, they were resisting male abuses. They were constantly active on their own and their kids’ behalf, jockeying for position in a female dominance order, competing over males, food, and territory, shielding their young from harm and trying to ensure that they would grow up into roles where (male or female) they would be dominant,
too. If some primate females had to live in a male world—and not all did—they would not just stand by; they would make the most of it.

In time, Hrdy realized that making the most of it in sex meant trying to exercise choice not just before mating, which was indeed often possible, but after mating as well. Like the diminutive gray mouse lemur, all primate females had options: mating opportunities beyond the first; “extra-pair” copulations (where there was a pair); adaptive or convenience polyandry; sex with other females; and, in the right circumstances, selective promiscuity. Even in pair-bonding species, where both parents contribute to offspring care, your chosen boy can get gobbled by a predator, fall out of a tree, be chased off by other males, or just move on to greener treetops. A girl can’t be too careful—she needs sexual insurance. And she also needs the best male genes her own sex appeal can buy. Growing evidence on all these points, throughout the animal world, led Hrdy to write a famous paper called “The Optimal Number of Fathers.” At this point you won’t be shocked to learn that the optimal number often isn’t one.

Not just in primates but also across mammals, the most impressive fathers are our not-too-distant relatives the small South American monkeys called marmosets and tamarinds. They live in the forest in small (although not always conventional) families in which fathers are permanent and do a wealth of parenting. Except for occasional twins, having one tot at a time is a primate hallmark, enabling a long, slow course of parenting and learning. But marmosets give birth to twins routinely, a feat possible mainly because of fathers.

It’s no easy task to keep twins alive in nature. Even in human populations, before modern times, fewer children survived from one hundred pairs of twins—that’s two hundred babies—than from one hundred single births. That is, twins died more than twice as often as singletons, which explains why human twinning was historically
rare. Selection worked against it, despite the apparent advantage of doubling your progeny.

But along the evolutionary way, marmosets stumbled on a trick to get around this: be the most involved fathers in the whole mammal world. They can’t get pregnant or breast-feed—even
they
couldn’t evolve a way out of 200 million years of biology—but they do everything else. In their thick, high forest realm, where infants would fall to their deaths or be picked off by a hawk or snake if left alone for a few minutes, they aren’t—not even for seconds—because anytime the twins are not suckling on their mother, they are riding dad. That’s twenty-four/seven, except for short milky interludes, carrying twins whose combined weight is 20 percent of his and counting, while in the daylight hours constantly moving through the trees and trying to find enough food to stay alive and pay the huge caloric bill.

Now, the marmoset mom’s life is no picnic, either. She has to find food for three, after carrying the twins inside her for months and enduring the risk of delivery. They’re 20 percent of her size, too; it’s as if
we
routinely gave birth to two fifteen-pounders, who proceeded to grow apace and breast-feed to their hearts’ content. But of the dozens of monkey species around the world, only these few can afford twins consistently, because the burden is as shared as it is in any pair-bonding bird. And although Mom and Dad are not winging it to and fro between food sites and a nest, they are bearing a big load. In fact, in some species of marmosets, families are made up not just of two parents but helpers as well—semi- or even fully adult males or females who refrain from reproduction while caring for the main pair’s young.