Women After All: Sex, Evolution, and the End of Male Supremacy (16 page)

Bonobos are not only less violent than chimps, more female-forward, and much more varied and affectionate in their sexual habits; they are also more socially positive and altruistic, even toward strangers. But how do these differences come about? Victoria Wobber, Vanessa Woods, Elisabetta Palagi, and others have in the last few years begun to study their development and have found the patterns in infancy; the two species differ very early on, which means the divergences could be hardwired.

New studies have opened the era of neurobiology and genomics of these striking differences between species. James Rilling and his colleagues, beginning in 2012, compared chimpanzee and bonobo brains using diffusion tensor imaging (DTI). In this technique, vivid colorized images show the orientation and size of the brain’s connections in three-dimensional space. Since the connections are white matter, DTI also indirectly reveals gray matter volume. Bonobos had more gray matter in limbic system areas related to emotion, in particular certain regions in the right brain known to
be involved in social life—including sexual behavior, social play, tolerance, and empathy, all of which are more common in bonobos. Strong connections linking the amygdala, which is involved in aggression, and part of the frontal lobe, which controls impulses, as well as part of the cingulate cortex, could easily enable bonobos to suppress aggression and feel empathy. The researchers go so far as to suggest an empathy “deficit” in the chimp brain. Put more positively, bonobos have brains that are anatomically more adapted for social cognition, empathy, and impulse control.

Ideally, we will soon progress to studies of gene expression—like those we saw in voles and mosquito fish, but noninvasive—that will explain these anatomical differences while linking the circuits to behavior. We are not there yet, although a great stride forward was made in 2012, when the first bonobo genome was published. This was long awaited, not because of an exotic curiosity about an endangered ape but because the triangulation of the human genome with those of our two cousins will yield insights into human traits and their basis in genes and the brain.

Even the early analyses, however, have found interesting things. First, bonobos and chimps have separated only one or two million years ago, less time than we thought for their big differences to evolve. Second, at least 97 percent of all genes are shared by all three species. Third, 1.6 percent of the human genome is more closely related to the bonobo genome than to the chimpanzee genome, while a different 1.7 percent is more like that of the chimp. Finally, for more than 3 percent of our genes, we are more closely related to one or the other than the two of them are to each other. These discoveries are a first step toward answering the questions that have most intrigued us about them: Are we more like bonobos or like chimps? How much did the last common ancestor of the two of them resemble either as they are today? And what was the common ancestor of all three of us like? Along the way, the answers to these questions will help reveal the brain genes that have made us, happily, more like the bonobos
in sex, play, and empathy and, unhappily, more like the chimps in individual violence and territorial aggression.

But what about male dominance and abuse of females? Which species are we more like in that? The answer turns out to hinge on where in human history you try to find it, and we will now explore that history.

Chapter 5

♦

Equal Origins?

C
amille Paglia began her masterful book
Sexual Personae
with “In the beginning there was nature.” She continued: “Sex is a subset to nature. Sex is the natural in man. Society is an artificial construction, a defense against nature’s power. . . . Human beings are not nature’s favorites. We are merely one of a multitude of species. . . . Nature has a master agenda we can only dimly know.” We are trying here to know it a little. Having followed evolution up to our closest relatives, we next come to ourselves.

The first phase of our evolution, hunting and gathering, lasted until about 10,000 years ago. Since fully modern humans, in terms of body and brain, arose between 200,000 and 100,000 years ago, we have lived the vast majority of our time on this planet doing what the few remaining hunter-gatherers do. In fact, we were doing it before we became fully human—
Homo sapiens sapiens.
This pointed repetition of the Latin word for “wise” may seem like special pleading, but this is what we call ourselves. This means you and me, but it also means any member of our species who has walked the earth in at least the last 100,000 years. That includes all hunter-gatherers
and other “primitive” people studied by anthropologists.

It’s important to understand this: when we say that hunter-gatherers inform us about our past, it’s not because we think they are relics of that past. Countless studies have shown that for all intents and purposes, they are biologically and psychologically just like us. The differences are cultural and ecological, not evolutionary or genetic. Their special interest derives from the fact that—for circumstantial reasons—they persisted in living as we all once did. So in studying them, we can watch our bodies and minds operate in our ancestral environments. In a way, they are our avatars to the past.

Notice that I put “environments” in the plural. We can’t talk about
an
ancestral environment; there were many in time and space in those 100,000 years. But the range of those environments does not include what has happened since the invention of agriculture. When we consider the change since the emergence of what we like to call civilization, the contrast is greater, and when we consider the last few centuries, greater still. As we’ll see, these changes were not all for the better, and one of the worst was what happened to relations between the sexes. For most of the history of our species, women were in a stronger position than they have been since—stronger, at least, than in almost all subsequent cultures until the last few decades in some postindustrial states. Even these latter-day safe havens for women have a long way to go to achieve gender equality. Hunter-gatherers, too, were far from perfect in this regard, but they were more egalitarian than we have been for thousands of years.

If I have succeeded so far in this book, you will already be convinced that the arrangements we humans have made for male and female sexuality and power are scarcely the only way to go. In fact, the opposite is true: the variety in nature is tremendous. But overall, males are nowhere near as necessary as females; as we’ve seen, females were the first sex, and any type of sex involves conflict as well as cooperation. In some species males predominate, in others females,
and in others the tasks of reproduction are shared about equally. There are species where males have been eliminated, but the same cannot be said of females. Maleness and femaleness rest on evolutionary and biological foundations, but they are not immutable, and there are many lessons to be learned about them from observing the natural world, if we keep our minds open.

If I succeed in the rest of my argument, I hope by the end to have convinced you that what we think of as male supremacy throughout past history was actually a rather late development in human evolution and will ultimately turn out to have been a temporary social adaptation. It was maladaptive in the deeper, more durable past, and it is maladaptive now, going forward. But first we must retrace the steps by which our last common ancestor (LCA) with bonobos and chimpanzees turned into the fully modern humans that we were by 100,000 years ago, and think about some of the biological, especially sexual, novelties that this transformation gave us.

The LCA—let’s call her Laca—was an ape that lived six to ten million years ago in Africa. We don’t know exactly what Laca was like, but she was one among many ape species that had by then been successful for millions of years. She was at home either in the trees or on the ground, climbing or walking on all fours with grasping hands and feet, and had a brain that was ape-sized or smaller. Something made upright walking an advantage for Laca; viable theories include being able to carry things, seeing farther, displaying newly evolving breasts or (for her partner) genitals, and reducing the heat absorbed from the sun. Modern apes and even monkeys do upright walking at times for some of these purposes. We know it had little to do with making stone tools, since they didn’t appear until perhaps two million years ago, and the same is true for big brains.

My favorite hypothesis is that it was good for carrying babies. Great ape mothers walk three-leggedly after their infants are born, using one hand to support the child. Monkeys hardly ever have to do
this, because even their newborns cling well. A monkey mother can unceremoniously start walking with a baby in her lap and the baby will reflexively cling to her with all four limbs. Great ape mothers have to provide support for the first few weeks, and this would have turned into infant carrying as upright posture evolved. It would also have allowed for a more helpless infant, born earlier because of a pelvis made for bipedal walking.

In any case, upright walking must have been a good thing, since several different species had evolved it by at least five million years ago.
Ardipithecus ramidus—
“Ardi” for short—is our most likely ancestor from that era. Ardi was about four feet tall, with long arms, a pelvis that proves she walked upright, and a still ape-sized brain, but with feet partly adapted for grasping. In other words, she was just what you’d like to see in a missing link. But perhaps Ardi’s most interesting feature was that she was not significantly smaller than her mate. Not only were the male and female about the same size—you can sex fossils by the angle between the bones that come down from the pubis, among other ways—but his canine teeth were also no larger than hers.

As we know (ever since Darwin), species with intense male competition for females are more likely to have males substantially larger than females. These tend to be species (like the elephant seal and red deer) in which dominant males get most of the sex after a tournament-like contest. They may have harems or simply monopolize females in a larger group. Among monkeys and apes, the males in such species tend to have large, sharp canines. Large body size differences between males and females—“sexual dimorphism”—occur in baboons, orangutans, and gorillas. Gibbons, which tend toward monogamy or even polyandry, have less of a sex difference than humans.

Bonobos and chimps have much less of a sex difference than gorillas but a bit more than us. Males in both species, though, have very large testicles compared with gorillas’, probably because gorillas
have harems, while bonobo and chimp females mate with multiple males. Either way, males compete. Gorillas strive to get mates into their harems and don’t have to worry too much after that, so
they
are huge, but their testicles aren’t. Chimps and bonobos compete much more for access to eggs, since fertile females blithely recruit the sperm of multiple males, which then vie with one another in a huge microscopic swimming match that often, in the end, comes down to sheer numbers.

So mating anatomy can take strange turns. Testicles don’t fossilize, but sex differences in body and, especially, canine size can point to mating patterns. Michael Plavcan has studied this in detail; in 2012, he concluded, “Although strong dimorphism is consistently associated with polygyny and intense male-male competition, a lack of dimorphism is not associated with any single mating system.” Despite these doubts, those studying Ardi argue for low levels of male-male competition—perhaps even monogamy, with substantial paternal care.

Either way, our next likely ancestor, probably descended from Ardi and common in Africa around a million years later, may have had males much larger than females. That was the famous “Lucy” species,
Australopithecus afarensis,
more fully upright than Ardi but brainwise (yet again) no more than an ape. Controversy continues about whether Lucy was substantially smaller than her mate. Ditto for the first two species of
our
genus,
Homo
—the evidence is confusing. But the later species of
Homo,
including Neanderthals, had a size difference no larger than ours. Canine size differences mattered less and less as we evolved, because our ancestors were now making stone tools and weapons. If they wanted to scare and tear, they did not need canines.

Chimps and bonobos teach us that big differences in mating habits and gender roles can arise in only a million years, and voles suggest that one genetic mutation can make the difference between a species with couples and fatherhood and a closely related species with
neither. This should give us pause when we talk about fossils spanning six or more million years. In that time frame, mating systems might come and go and female fortunes rise and fall with them.

Since the beginning of the transition from hunting and gathering to other forms of social and economic organization, there has been less genetic change, and none that affects our basic biology. When we talk about physical gender in fully modern humans, we know what we mean: a species with males on average 7 percent taller and 15 percent heavier than females, with little difference in canine size; men with more visible facial and body hair, broader shoulders, and greater muscle mass; women with wider hips, more fat surrounding them, and visible breasts (unlike apes, who have only nipples, except when nursing). Also, girls mature and show their adult anatomy sooner than boys do.

Reproductively, human females have two more key adaptations: first, many years of life after cycling stops and, second, well-concealed ovulation. Primates generally have a less distinct estrus than other mammals, but some (chimps and bonobos included) have sexual swelling and clear behavioral signs of receptivity; we have nothing nearly as obvious. It used to be said that human females had evolved continuous sexual receptivity, but this phrase was evidently coined by hopeful male scientists; what they probably meant was that women are randomly receptive across the days of the monthly cycle.