Significant Others: The Ape-Human Continuum and the Quest for Human Nature

Significant Others: The Ape-Human Continuum and the Quest for Human Nature

by Craig B. Stanford

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In Significant Others, the co-director of the world-famous Jane Goodall Research Center uses our recent knowledge of great ape behavior to examine (and puncture) many myths about humans-about infanticide, mating practices, the origins of human cognition, the human diet, language, and many other subjects. Evolutionary scientists know that the dividing line between


In Significant Others, the co-director of the world-famous Jane Goodall Research Center uses our recent knowledge of great ape behavior to examine (and puncture) many myths about humans-about infanticide, mating practices, the origins of human cognition, the human diet, language, and many other subjects. Evolutionary scientists know that the dividing line between humans and other animals has grown increasingly blurry-it's even become a cliché to note that we share 99 percent of our genes with chimpanzees. Yet this knowledge, while superficially accepted, has not really been absorbed by many fields, especially the social sciences. At the same time, the knowledge that all humans are genetically and cognitively modern, no matter how "primitive" we may find them, has left the apes the only true "savages." Thus if we want to learn about human nature and how we came to be as we are, we have to look to the apes to tell us.This is a sweeping, fresh, controversial book on what the science of primates can tell us about our own natures.

Editorial Reviews

Douglas Foster
Significant Others is an engaging overview of research about apes.
Los Angeles Times
Paul Chance
Stanford . . . shows that there are important parallels between ourselves and our hirsute cousins. . . . [and] makes his case in a highly readable form. . . . Anyone with an interest in humans or apes will find this book a fascinating read.
Psychology Today

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Part I: Food, Love and Death


Our closest relatives, the chimpanzee and the bonobo, are the link between the fossil record and the living past. This makes field research on them extremely important and gives added significance to debates over the meaning of their behavior. It happens that the behaviors currently most debated in chimpanzees and bonobos include two old favorites of humanity, sex and violence.

In a sun-dappled glade in a forest in Tanzania, a female chimpanzee sits on a tree limb munching a handful of figs. From her rump hangs her sexual swelling, a football-sized fluid-filled sac advertising her fertility. On the forest floor below, a male chimpanzee watches her intently. Every few minutes he reaches over to a nearby bush, shakes it like a baby rattle, and glances up at the female. The shaking is a courtship gesture, an invitation to mate recognized by the female and all other members of the community who are present. But at this moment our female is preoccupied with her lunch and does not respond to the male by presenting her swelling to him to copulate, as he expects. As she continues to ignore him, his bush-shaking mating demands grow more rapid, until in a pique of sexual frustration he charges up the tree toward the female. She screams loudly and retreats higher into the tree crown, leaping across to an adjacent tree with the male in hot pursuit. In seconds he catches up with her and gives her a sound pummeling with his fists and feet while she screams in terror. In the end she submits to him; the male gets his brutal tryst and walks away, leaving the female shaken and bruised. Another continent, another ape: A female bonobo in the San Diego Zoo is facing a similar turn of events. Today her sexual swelling is at peak dimensions, a vivid billboard of her availability. But at this moment she is busy with her lunch and not interested in the attentions of the dominant male in her group. He approaches and waits for her to present her swelling to him for sex, but she continues eating her broccoli and carrots. He angrily hits out at her, attempting to force her into action. She screams and beats a momentary retreat. This time, however, there are reinforcements. The female is quickly joined by a trio of other adult females, and the quartet treat the nuisance male like a sexual miscreant, attacking him and sending him packing with several cuts made by their canine teeth on his shoulders. A reminder that sisterhood is powerful....

Chimpanzees aren't what they used to be. For hundreds of years, they served us as funhouse mirrors of who we once were and what we might have become had evolution taken a different course. Among the four great ape species, chimpanzees received the lion's share of attention as models of early humanity. But until the 1960's, we didn't really know much about their lives. Then Jane Goodall set out for Tanzania to study them in the wild for the first time. Chimpanzees turned out to be more than extraordinarily smart animals; they shocked us with their complex societies, tool-using abilities, and love of raw meat. Goodall's research turned our view of chimpanzees, and in turn of ourselves, on its head. The behaviors documented by field researchers since Goodall's early days include intercommunity warfare with lethal territorial aggression, cooperative hunting for other mammals, with the spoils of the hunt ritually shared and used for political and sexual barter, and the manufacture and use of a wide variety of tools made of wood and plant products, and also of stone in some sites.1 Gorillas and orangutans, the cousins of both chimpanzees and ourselves, have received vastly less attention from scientists than chimpanzees or bonobos have, mainly because of the perception that chimps and bonobos have more human-like intelligence.

But chimpanzees aren't what they used to be. Goodall's first reports that chimpanzees are not vegetarian pacifists came as a shock in anthropological circles. Some scholars even alleged that the lethal aggression seen during encounters between neighboring social groups was aberrant behavior, occurring only in animals disturbed by human contact.2 But as the field data accumulated it became clear that the brutal side of chimpanzees is quite real. Males strive to ascend a rigid dominance hierarchy, and upon reaching high rank they wield their political power with Machiavellian cunning worthy of a Shakespearean conspirator. Sexual coercion and beating of females who do not submit to male desires is routine. Males patrol the perimeter of their territory, attacking and sometimes murdering their unwary neighbors. In the 1970's, chimpanzees at two study sites in Tanzania, Gombe National Park and Mahale National Park, were observed to fission into two separate communities, after which the larger community in each case systematically exterminated the smaller one. This "warfare" has been seen in only two primate species -- humans and chimpanzees.

Chimpanzees are also efficient and ruthless predators whose prey includes monkeys, antelope and wild pigs at some study sites. Their attacks on red colobus monkeys are brutal and heartstopping. In the early and mid 1990s I conducted field research on wild chimpanzees to learn more about the predator-prey relationship between chimpanzees and colobus.3 Colobus monkeys are attacked by hunting parties of chimps, and the male colobus defend their groups by courageously counterattacking their ape marauders. The ensuing hand-to-hand combat is usually won by the chimps. Once captured, the monkeys are killed either by a bite to the neck (for small-bodied juveniles) or by thrashing them against the ground or a tree limb (for adult colobus). Nearly all kills are made by males, and after a successful hunt the meat is controlled by the high-ranking males in the hunting party. These honchos control the distribution of the meat in Machiavellian ways: they share with allies and kin, and withhold the bounty from rivals. They use meat to entice ovulating females to mate with them - an orgy of meat-eating and sex straight out of Tom Jones.

Meanwhile, only since the mid-1980's has the closely related bonobo come to serve as an evolutionary counterpoint to chimpanzees. They may look very much like chimpanzees (their former English name, pygmy chimpanzee, was a misnomer based on their relatively slender proportions), but bonobos are an ape of a different flavor. In sharp contrast to hierarchical chimpanzee society, studies of bonobo behavior have revealed a society molded by cooperation, recreational sex as social communication, and alliance formation rather than war and aggression. As primatologist Frans de Waal of Emory University puts it, "The high points of bonobo intellectual life are found not in cooperative hunting or strategies to achieve dominance but in conflict resolution and sensitivity to others."4 Female bonobos band together in coalitions to dominate males, avoiding the sexual coercion that male chimpanzees routinely inflict upon their females. Such behavior among females is nearly unknown in chimpanzees; in the latter, males are sociable and supportive among themselves, and their bonds are both the cause and consequence of everything from communal hunting to the fierce defense of their territorial borders. Female bonobos even tend to dominate in some circumstances. Primatologist Amy Parish of the University of Southern California studied female bonobos at the San Diego Wild Animal Park and found that females routinely displaced males over feeding opportunities, often through coalitions that also prevented harassment by males.5 Then there is the sex. Bonobos are known, more than anything else, as the sexy ape. They are said to mate more often, in more positions, with more recreational intent, then any mammal other know who. They engage in homosexual pairings, in which two females rub their genital swellings together ("GG rubbing" in the lexicon of bonobo researchers), in order to ease tensions between individuals and perhaps allow them to feed near one another without undue stress. This female bonding is absent in chimpanzee society. Males also like to rub genitals with one another. Even during male-female pairings, bonobos take the sexual act to new primate heights. Coupling occurs in a wide variety of positions; de Waal reported that among captive bonobos, the female sometimes gestures mating instructions to the male.

An even more striking difference between female chimpanzees and bonobos is said to link the latter most closely to the human family tree. The females of nearly all mammalian species are reproductively active only during a few days surrounding ovulation. This estrus period characterizes all of the higher primates, except of course humans. Females of our species, while more likely to conceive around the time of ovulation, are freed from any strictly defined period of "heat." The result has been that sex serves not only for procreation but also as a mechanism of social communication and reinforcement of long-term pair bonds. This release from the stricture of estrus is thought to have been a pivotal event in the evolution of human society, perhaps connected to the concealment in human females of the exact timing of ovulation. Males are always interested in sex, but especially so when the chances are greatest to conceive an offspring and further their reproductive output. If a male can detect when ovulation is occurring in his mate, he has little need to spend the rest of her cycle attending to her. They would therefore, the thinking goes, have stayed with females and provided support for them and their offspring only if ovulation were concealed, in order to ensure being the father of her offspring.6 Bonobo females are often said to be the only mammals other than ourselves to be released from the bonds of estrus. They maintain their sexual swellings for a much longer portion of their menstrual cycles than chimpanzees do, and therefore, like humans, mate nearly throughout the cycle. Since the female primate typically shows no interest in mating except when she can conceive, cycling for a longer portion of the menstrual cycle translates into more sex and thus more opportunities to use sexual access for all manner of social communication and non-procreative bonding. Female bonobos carry their sexual swellings proudly for some two weeks at a time (several days longer per month than female chimpanzees do), making it hard for males to detect exactly when a female is most fertile. Being released from estrus, bonobos have come, like humans, to use sex as much for communicating with males as for conceiving offspring.

And bonobos have been reported to simply do it more often than chimpanzees do. Copulation rates recorded by de Waal and Parish for captive bonobos in the San Diego Zoo and at the Yerkes Regional Primate Center in Atlanta are sky-high compared to those among any wild chimpanzees that have been studied. This observation, combined with the lesser degree of male dominance in bonobo society, has led de Waal to write, "The chimpanzee resolves sexual issues with power; the bonobo resolves power issues with sex."

In war as in romance, bonobos and chimpanzees appear to be strikingly different. When two bonobo communities meet at a range boundary at Wamba, a research site in the lowland rain forests of the Democratic Republic of Congo, famed bonobo researcher Takayoshi Kano observed that not only is there no lethal aggression, as sometimes occurs in chimps, there may be socializing and even sex between females and the enemy community's males.7 But if bonobos appear to make love, not war, this is not exactly true. Although studies of skeletal pathology show that adult bonobos incur fewer injuries at the hands of their group mates than either chimpanzees or gorillas do,8 they are not entirely peace-loving. About half of all the intercommunity encounters seen by Kano's team involved aggression of some sort. The difference is that bonobo attacks and injuries are often directed by females at males, rather than the reverse as in chimpanzees. There are even reports from zoos of female bonobos brutalizing a male so badly that his penis was severed.9 Hunting and meat-eating, which chimpanzees so relish, provides a final striking contrast. Bonobos catch monkeys in their rainforest habitat almost as well as chimpanzees do, but they don't seem to know what to do with them. Bonobos will use captured baby monkeys as dolls or playthings for hours, only to release them unharmed (though worse for the wear) when they become bored.10 It's as if the protein and fat value of the prey hasn't dawned on their kinder, gentler sensibility.

These recent findings about bonobos have led anthropologists to place humans squarely at an evolutionary crossroads. One path leads to a chimpanzee world of male brutality and violence, where might makes right and the low guy on the totem pole must grovel to avoid taking a beating from his higher-ups. The other path leads to a kinder, gentler vision of humanity in which violence is not strength and compassionate bonding is not weakness. It's not Camelot, it's bonobo society.

This starkly black-and-white view of the two apes has become entrenched in the minds of both the public and of many scientists. Sexy apes versus brutal ones represents an appealing dichotomy - our evolutionary options laid out in simple terms. It may be high time, however, to throw some cold water on the lurid descriptions of bonobo sexuality. Captive bonobos are hypersexual - far exceeding their chimpanzee kin in both the quantity and quality of their couplings - but whether this accurately reflects the behavior of wild bonobos is another question. Although it is clear that bonobo social behavior differs in several fundamental aspects from that of chimpanzees - most notably in the bonds that form between females - many of these stark contrasts have been based on comparisons of wild chimpanzees with captive bonobos. Most of the bonobo observations come from the San Diego Zoo and Yerkes Regional Primate Center. Animals in captive settings are well known to display greater frequencies of the whole gamut of social behavior - from fighting to sex - than do their wild counterparts.

There is often little else to do in captivity, where animals are in enforced proximity and have no need to spend their day foraging for food. Their behavior patterns do not necessarily reflect those that evolved for living in an African forest.11 Instead of comparing bonobos in labs or zoos with chimpanzees in the wild, we should more appropriately turn to wild bonobo populations. While they are far less studied than chimps, we know about natural patterns of bonobo behavior from two long term study sites in the Democratic Republic of the Congo: Wamba, the site directed by Kano, and Lomako, which has been occupied by two separate research teams from the United States and Germany. The field data show that in two important respects, female bonobos are no more erotic than their chimpanzee counterparts. First, the frequency of copulating, in which captive bonobos show a markedly higher rate than wild chimpanzees, is no different at all between wild bonobos from Wamba and wild chimps at either Tanzanian site, Gombe or Mahale.12 Second, the idea that bonobo females are released from estrus is due to data on the duration of sexual swelling taken mainly from bonobos at Yerkes. There, in captivity, female bonobos maintain their sexual swelling for a lusty twenty-three days, nearly half of their forty-nine day estrus cycle.13 This dwarfs the receptive period of wild female chimpanzees from, say, Gombe, who swell for about thirteen days of their thirty-six day cycle. But this comparison changes completely if we consider wild bonobos rather than captive specimens, whose excellent nutrition may produce earlier menarche and a ratcheted-up reproductive cycling. Bonobos from Wamba in the Congo are swollen for only thirteen days of a thirty-three day cycle, numbers that are much closer to those of wild chimpanzees than they are to captives of their own species. A recent report of captive bonobos in Antwerp, Belgium shows that even in captivity bonobos do not necessarily have longer swelling durations than chimpanzees.14 The release from estrus that has been said to characterize bonobos is certainly less a feature of that species than some have argued.

Other aspects of bonobo behavior also bear a second look. Female bonobos, it is true, often dominate males, but this domination occurs in only two settings: over food and when sex is involved. Males often get sex by acceding to females' desire to feed, and so might be thought of as strategically submissive in select situations - cleverness through subordination is certainly not unknown in other primate societies. Meat-eating, while certainly less common than among chimpanzees, may be quite frequent among bonobos as well, but has been underrated because of the lack of field research. German researchers Barbara Fruth and Gottfried Hohmann have observed extensive meat-eating and meat-sharing by bonobos at Lomako. Yet most primatologists still refer to the bonobo as the "vegetarian" great ape.15 Before we tar ourselves with the legacy of the male-chauvinist, carnivorous, warring chimpanzees or congratulate ourselves for leaning toward the Venusian, sisterhood-is-powerful bonobos, we would do well to consider how our depiction of primate societies may be intertwined with our own political views. It is certainly not unheard of for research interpretations to be influenced by politics. As we saw in Chapter 1, in the 1960's the brotherhood of predominantly male anthropologists foisted the infamous Man the Hunter view of human origins upon students and the public alike, arguing that the prehistoric male role of bringing home the bacon accounted for the rapid expansion of the human brain. Not until several years later did female anthropologists weighed in with the reminder that something had to account for women's brains expanding too. It's no coincidence that this insight prevailed after the rise of feminist politics and increasing power and influence of women in the academic world since the 1960s. The original idea and its correction were both politically loaded. Meanwhile, research into the social lives of our great ape relatives continues. In the chapters that follow we will see that some of humanity's darkest traits show up in the spotlit glare of research on the behavior of apes and their close kin.

Meet the Author

Craig Stanford is Co-Director of the Jane Goodall Primate Research Center, in Gombe, Uganda; Director of the Bwindi-Impenetrable Great Ape Project, in Bwindi-Impenetrable National Park, Uganda; and Associate Professor of Anthropology at the University of Southern California. He splits his time between Uganda and Los Angeles, California.

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