Women After All: Sex, Evolution, and the End of Male Supremacy (15 page)

Years later, however, writing her scientific masterwork,
The Chimpanzees of Gombe,
she reported unpleasant findings that made them seem anything but gentle. Two in particular stood out. First, there were two females, a mother and her grown daughter, who took to killing other females’ infants. They did this not once or twice but many times, as if an obsessive and grim pathology had taken hold of them. This was not like the langurs, in which foreign males enhanced their reproductive success by killing the infants of other males and later impregnating the females. But it did resemble the patterns of infanticide in some species—wild dogs, for instance—in which females kill others’ young, with the effect of making room and resources available for their own.

Equally disturbing and in the end more common was a pattern now widely seen and studied in wild chimpanzees across Africa. A number of chimp males—a gang, really—patrols the edge of the group’s territory in the forest. If in their travels they happen upon a member of a neighboring group, they promptly set upon that chimp en masse and beat, kick, bite, and stomp him to death. Over time, one group may eliminate another and take over the victims’ territory. This habit was almost human in a very different sense, and it was not welcome news, coming from a species that is literally our next of kin; in DNA sequence, we are about 98 percent chimpanzee.

The pattern has been confirmed many times in different chimp populations. John Mitani, one of the leading field primatologists in the generation following Goodall, reviewed the findings in 2009. By then long-term studies had been in place not only in Gombe but in the Mahale Mountains (also in Tanzania), in the Budongo Forest and the Kibale National Park (both in Uganda), in Boussou in Guinea, and in the Taï Forest of Côte d’Ivoire. Kibale has long-term studies of two separate chimp communities, and more recent work has begun at Mount Assirik, in Senegal, and in the Republic of the Congo. So now we have decades of
data on chimp groups in forests, mountains, dry savannas, and blends of these, from East to West Africa across thousands of miles. We have history. All of this information has revealed specific adaptations, variation that is both genetic and cultural, and yet also some persistent findings.

Competition between males, both within and between communities, is routine, partly because chimp females have obvious estrus, which makes what is called the operational sex ratio—the number of males who might want to mate with a
receptive
female at a given time—very high. Dominance is critical; by genetic evidence, a third to half of all infants are sired by the single male at the top during his tenure. Male coalitions make all the difference, and these alliances trump pure physical strength. The half or more of the mating opportunities that the alpha male doesn’t get, he cedes to his coalition partners. Dominant coalitions have lasted up to seven years, punishing and pushing back challengers in the group. Eventually, as dominants age, coalitions can’t keep command, and a revolutionary alliance may arise.

A second function of male coalitions is hunting, seen in several different forest chimp communities. Red colobus monkeys are typical prey, and chimp males do best when they strategically deploy to ambush a stray colobus in the trees. These hunts can seem deliberate and coordinated and can last five or six hours. Brave little colobus monkeys may mob the chimp males and even wound them, but hunts often succeed, and the meat is shared. This is a clue to the evolution of human sharing, since meat is the food most often shared among hunter-gatherers. The chimp version looks more like tolerated scrounging, and that may be where human sharing came from. Geza Teleki, Craig Stanford, and others proposed that male chimps would trade meat for sex, but in some environments they don’t especially share with estrus females.

However, this may depend on local ecology or tradition. Cristina Gomes and Christophe Boesch reported in 2011 that in Côte
d’Ivoire’s Taï Forest, chimp males
do
trade meat for sex. In fact, meat for sex was one deal among several in a complex ape economy. In their sophisticated quantitative analysis, grooming and support in dominance challenges mattered, too. Grooming removes nits, which benefits the groomee and probably also releases endorphins, as a result of fur stroking. The groom
er
gets the tasty tidbit, but the benefits don’t stop there, because grooming tends to be reciprocal: you stroke me and I’ll stroke you soon enough. Also, chimps trade social support in frequent disputes. But they also trade
across
commodities. In particular, males exchange meat for support from other males, and females in estrus exchange sex for meat—they mate more with males that share it. If they didn’t, females would almost never eat meat, and low-ranking males would have little chance of ever having sex.

So even in the man’s world of chimp society, females influence which male gets to them. Rebecca Stumpf and Christophe Boesch showed that Taï Forest females exercise choice—meat sharing being one standard males have to meet. Focusing on the most fertile part of estrus, they found that active seduction—she may repeatedly offer her prized swollen, pink rump to her chosen beau-for-a-day—does affect who mates when. In almost a thousand sexual encounters, males were the initiators three out of four times. But of these male attempts, females resisted nearly three in ten and mostly succeeded in putting off the male’s advances. In the quarter of encounters when
females
did the seducing, males gave in to temptation eight out of ten times. Females also get to say when sex ends, allowing longer copulations with males they like; in a promiscuous mating system, where males have evolved huge testicles to trump the sperm of rival males, this female stopwatch can make all the difference.

But if chimps are our close relatives, what does all this bad male behavior say about us? Before we answer that, we have another, very different cousin equally close by. That’s the bonobo, and if we are roughly 98 percent chimpanzee, we are also 98 percent bonobo.
How did we end up with two different species that are both our next of kin? Well,
their
ancestor split from
us
around seven million years ago, but they’ve been separate from each other for only a million or two—since the Congo River formed and separated what we might call the chimpobos from the bonozees. Being poor swimmers, the two populations said their good-byes and in due course became chimps and bonobos. But after that short one or two million years, they were dramatically different in their behavior. So how do we sort out which is the right mirror for us?

It helps greatly that in 2012 Kay Prüfer and his colleagues sequenced the bonobo genome. We had the human genome in 2000, the chimp in 2005. Now that we have all three, geneticists can triangulate the comparisons and find out just which genes chimps and bonobos don’t share with each other and which we humans do or don’t share with either or both. But this will take time. In the meanwhile, ongoing research in African habitats is telling us a huge amount about behavior.

There are many similarities. Chimpanzees and bonobos look like relatives and overlap greatly in body size, although bonobos don’t get as large as the largest male chimps. Bonobos have darker fur, puffy around the head, and the head itself is smaller. As Adrienne Zihlman showed decades ago, the relative length of the limbs—shorter arms, longer legs—is more humanlike in bonobos. Anatomically those are the main differences. But in behavior and reproduction, it’s a whole other story.

Bonobos remain confined below the Congo River’s big bend, where (because the most dangerous species is us, with our endless wars) they have not been easy to study in the wild. Yet this research has been done for many years, and it has been an ongoing revelation. In a sense, you could take chimp sex and violence and flip them. “Make love, not war” became a cliché about bonobos
.
It’s a stretch to say “love” about an ape’s subjective experience, but whether it’s love, lust, or a mellow blend, it’s clearly female-forward. It’s almost
as if the lemur syndrome somehow got from Madagascar to the Congo, leaping over the male chauvinist societies of baboons and chimpanzees to inspire this isolated population south of the Congo River, whose members are living lives we humans might aspire to.

Consider: bonobo females are not exactly dominant over males, but they make alliances themselves that give any would-be uppity male long pause before trying to dominate
them
. These coalitions may once have functioned the way the cabals of male baboons do, keeping the most aggressive, especially younger boys, in line. In any case, what we now see in bonobos is a much lower level of male aggression against females
and
fewer violent conflicts with other males. Not for them a periodic, gang-style, testosterone-charged patrol into the forest looking for hapless victims from a neighboring group. Not for them, either, mortal fights among themselves over access to females in estrus. And certainly not for them: coercing females into sex.

We didn’t need the genome to understand that different physiology helped make all of this possible. Female bonobos do have estrus, but compared to chimps’ it is anatomically less dramatic and behaviorally more spread out. They have sexual swelling, when they are more likely fertile, but it lasts longer and is mimicked by pseudoestrus—swelling without fertility—during pregnancy and the postpartum period. Even in real estrus, maximum swelling does not always cue ovulation. On a graph, female sexual behavior (such as soliciting males) seems smeared across many more days of the month in bonobos than in chimps. So males have much less of a signal as to when ovulation really occurs and much less incentive to provoke fights. They also get more sex, as several females are likely receptive on any given day.

But here is where bonobo females get the widest choice of all: when they incline toward sex, they don’t have to choose males. They can and often do choose each other. Vulva rubbing is a common and favored pastime among females; sights and sounds go along with
it that seem to denote pleasure and may reflect a kind of orgasm. Female bonds are strengthened by this intimacy—“friends with benefits” seems apt—and wider alliances are enhanced. Since (as in chimps) it’s the females that change groups after puberty, these trysts help build strong relationships among females who may initially be strangers.

But males don’t suffer as a result. Apparently there is enough desire to go around, and males can have plenty of leisurely sex with the same females. They occasionally have to fight or be on the alert, but they don’t have to get seriously hurt or killed, and they don’t have to languish in frustration while bigger, tougher males shove them aside. They just have to eat, drink, and be sexual. In fact, unlike other apes, bonobos combine the pleasures of food and sex, much as humans do. And they are the only apes that routinely have face-to-face intercourse, sometimes complete with broad, gratified-seeming smiles. For bonobos, the battle of the sexes is win-win. In addition to more sex and less violence, bonobos play in adulthood, something rare in chimpanzees. That makes them appear more human, since adult play has always been viewed as one of our best features. Finally, bonobos are altruistic in ways that chimps are not—ways that have also in the past seemed uniquely human; they share for the sake of being sociable, even with strangers.

If this portrait of bonobo society sounds too good to be true, perhaps it is—but only to this extent: all animal species have some conflict, and in every species sex is to some extent a cause. Compared to chimps, bonobos really are the “love, not war” species, and female coalitions get most of the credit. Nevertheless, they do have conflicts.

Gottfried Hohmann and Barbara Fruth studied wild bonobos in the Democratic Republic of the Congo (DRC), with more than fifteen hundred hours of observation from 1993 to 1998. They were interested in conflicts related to mating, so they analyzed observations
of mixed-sex groups, the most common kind. Defining aggression as pulling, slapping, hitting, and biting, they found 391 instances of conflict where the sex of both parties was known. Of these, 38 percent were between males, 26 percent were female-on-male, 23 percent were between females, and only 11 percent were males attacking females.

However, aggression was more likely on mating days, especially just before, during, and after mating. Both males and females who
started
conflicts had greater overall mating success than those who did not. Females often harassed other females’ mating attempts, and the harassment revolved around certain preferred males. Male-on-female aggression was unusual and confined to random interactions, not friendships, even though mating was more likely in the latter. Finally, male aggression against females did indeed produce retaliation by female groups, often supported by other males.

Compared to bonobos, chimps have much more male-on-female aggression, much less female-on-male, and variable amounts of same-sex fighting, but chimp male-male fighting is far more likely to be severe. As for bonobo mating success, rank does matter for both sexes, but since there is little male coercion, female choice is effective, perhaps paramount. Male violence is mitigated by male-female relationships. Martin Surbeck and his colleagues, in a 2012 hormonal study of wild bonobos, found that male aggression increased around fertile females, but only low-ranking males had increased testosterone. High-ranking males were often in ongoing relationships with females, had more sex, and didn’t need a testosterone boost to get it. The other times female bonobos tend to fight each other are, remarkably, contests over the dominance rank of their adult sons. So important is their influence in the bonobo social world that the next generation’s allotment of male power depends on it.

But what about sex between females? Zanna Clay and her colleagues published studies in 2011 and 2012, based on more than one thousand
hours of observations of semiwild bonobos in a DRC sanctuary. Clay studied all aspects of these erotic occasions but focused on copulation calls—high-frequency squeaks and screams. These were more likely with males but occurred during female sex, too. The 674 female genital contacts were not random: most were in pairs of low-ranking females, next between low- and high-ranking, and last (rarely) between high-ranking females. The squeaks and screams rang out in about one in five contacts, mostly given by low-ranking females, especially with high-ranking partners. Low-ranking females were much more active in same-sex trysts, but high-ranking ones were much more likely to initiate. And if an alpha female was watching (ape sex is usually public), this “audience effect” made the calls even more likely. So the call is not just something physical but reveals the excitement of certain social contexts—and it helps build key relationships. Newly arriving immigrants are sure to be low in rank, and these public intimacies are their entry point.