The Goodness Paradox: The Strange Relationship Between Virtue and Violence in Human Evolution by Richard Wrangham. Pantheon, 400 pages, $27.95.

By George Scialabba

On June 30, 1860, there was a debate in Oxford between Thomas Huxley, Darwin's chief explainer, and Bishop Samuel Wilberforce, himself a considerable intellectual. Concluding his skeptical remarks, Wilberforce turned to Huxley and asked mockingly whether it was through his grandfather or his grandmother that he claimed descent from an ape. Taking the podium, Huxley thundered that if he had to choose between having an ape for a grandfather or a clever and influential man who used his gifts to turn new scientific ideas to ridicule, he would certainly choose the ape. There were no more snide jokes about Darwinism in Victorian England.

Still, one feels for the Bishop. It was hard in 1860 to get one's mind around evolution by natural selection, and it still is. It's difficult talking about causation without purpose, but that is what Darwinism requires. And telling a story about the origins of morality that begins hundreds of thousands of years before any creature had a sense of right and wrong, or even a sense of self, is a tall order.

Richard Wrangham, a primatologist at Harvard, has spent his career studying the great apes, especially chimpanzees, bonobos, and us. He is perhaps best known for Catching Fire: How Cooking Made Us Human (2009). In that short but highly original book he argued that the discovery around 1.9 million years ago that applying fire to food makes it more palatable and digestible transformed human destiny. It did this biochemically, by vastly increasing the energy released by food when cooked, energy that fueled a large increase in the size of our brain. And it changed human destiny sociologically by giving rise to the sexual division of labor, and specifically marriage.

Wrangham's first book (co-authored with Dale Peterson), Demonic Males: Apes and the Origin of Human Violence (1996), is more continuous with the line of argument of his new book than Catching Fire is. Demonic Males was written in the wake of two momentous discoveries: of the violence of chimpanzees and of the pacifism of bonobos. In-depth study of chimpanzees began in the 1960s with Jane Goodall. It was not until the mid-1970s that chimp-on-chimp killings were observed and their pattern firmly established. The existence of bonobos was inferred from museum skeletons in 1928, but the first book about them based on observation came out in 1992, only a little before Demonic Males.

Much violence is adaptive, i.e., promotes survival. That may not seem controversial now, but it was through much of the 20^th century. Culture was thought to be the source of our anti-social emotions, and any suggestion that they had biological roots as well was considered politically retrograde, or at any rate too depressing to contemplate - as though inherited tendencies were irresistible and absolved those acting under their influence of all moral responsibility. It is not yet known - it may never be known - precisely how genes and culture interact to determine any complex behavior. But enough is known to vindicate the common-sense intuition that both matter. Our genes are not our doom.

Surveying the extensive record of primate violence in Demonic Males, Wrangham and Peterson made an intriguing discovery. Infanticide is not uncommon; and though adults - usually males - killing other adults of the same species is uncommon, it does happen. But in only two species do bands of males prowl the borders of their range and kill isolated members of other communities: chimpanzees and human hunter-gatherers. This is pure aggression, not territorial defense. The reason appears to be increased access to food resources and, when all the males of a neighboring community are killed or driven off, annexing the females. The record of chimpanzee violence is full and clear. Most remaining hunter-gatherer groups have been brought under the jurisdiction of a modern state and to some degree assimilated, so the record of human aggressiveness is more ambiguous. Still, as Wrangham and Peterson write, though "peaceful foragers have been repeatedly hoped for," they have very rarely been found.

What has been found, instead, are bonobos. The last of the great apes to be discovered, bonobos are so similar to chimpanzees physically that their skeletons lay in museums for fifty years before it was noticed that they were a separate species. But socially and behaviorally, chimps and bonobos are worlds apart, even though they only live on opposite banks of the Congo River. Unlike chimpanzees, bonobos do not patrol, do not raid, and do not kill their neighbors. The sometimes-deadly competition among males for sexual primacy and the rape and beating of females, which are commonplace among chimps, are unknown among bonobos. Neighboring bonobo communities can mix amicably, which almost never happens among chimpanzees. Sex is much more relaxed and, apparently, enjoyable.

What probably explains this unusual gentleness is a curious fact of bonobo biology. Males can't tell when females are ovulating, so there's no competition for fertile females. This seems to have left a power vacuum, which females filled. Bonobo society is female-dominated: if there is a fight between a male and a female, and the female calls for help, the females of the troop turn out and chase the male away.

How did this idyllic state of affairs come about? It turns out there is a relation between the abundance of food in an environment and the size and stability of foraging parties, and a further relation between the character of foraging parties and violence along the border between ranges. Scarcity has its usual malign effects. Why is the bonobos' environment more benign than the chimps'? Bonobos, chimps, and gorillas eat much the same foods: fruit, herbs, buds, leaves. But gorillas are more sensitive to dry spells, during which they move into the mountains, where there is greenery. In normal periods they compete for food with chimps. As it happens, there are no mountains south of the Congo River, so no gorillas live there, and the bonobo have the food supply all to themselves. "Bonobos have evolved in a forest that is kindlier in its food supply, and that allows them to be kindly, too."

Humans seem to have a capacity for violent aggression as strong as that of chimpanzees and a capacity for gentleness and docility as strong as that of bonobos. "Compared with other primates, we practice exceptionally low levels of violence in our day-to-day-lives, yet we achieve exceptionally high rates of death from violence in our wars. That discrepancy is the goodness paradox." Wrangham has been pondering this paradox in the twenty years since Demonic Males and has the first draft of an explanation. It is, literally, far-fetched, relying on observations from Siberia, the South Pacific, the Amazon, Tierra del Fuego, and other remote corners of the earth, as well as on the work of archaeologists, paleontologists, psychologists, biochemists, neurophysiologists, geneticists, and others. Whether or not Wrangham is right - and no theory this complex and ambitious is ever more than partly right - there is something impressive, even moving, about the book's sifting, weighing, and fitting together of evidence from a half-dozen continents, a dozen disciplines, several dozen species, and two million years into a large and intricate structure. The clichés about science being a vast cooperative endeavor may actually be true.

Scientists classify aggression into reactive and proactive types. Reactive aggression is a response to a provocation or threat. It's hot-blooded, angry, impulsive and associated with high levels of testosterone. Proactive aggression is cold-blooded, calculating, premeditated, strategic. Think of those TV westerns where the hero deliberately provokes a slow-witted, hot-headed, clumsy antagonist who goes for his gun while our hero pulls his hat down over his eyes and clobbers him over the head with a six-shooter. Our hero is proactively aggressive, the villain reactively aggressive. Usually, reactive aggression is individual; proactive aggression institutional: eg, war and capital punishment.

The types of aggression constitute one building block of Wrangham's theory of moral origins. An equally important element of that theory is domestication, which turns out to be a crucial category for interpreting the human evolutionary past. For a long time, practical knowledge about domestication outran scientific understanding. Breeders of horses, dogs, and pigeons reliably obtained results. But no theory of human domestication was thought to be necessary, even by Darwin, on the apparently self-evident ground that domestication requires someone to direct the process, like the breeder, and obviously no one had done that to humans.

But while breeding, or artificial selection, requires an external agent, natural selection does not. If selection pressures work against aggressiveness, animals will self-domesticate. That humans have self-domesticated has grown increasingly obvious over the last half-century. Even apart from increased docility - the primary index of domestication - humans show many signs of what has come to be recognized as the domestication syndrome. Some of those signs appear only in animals, like floppy ears, white spots on forehead fur, curly tails, and white feet - all of them rarely or never found on the animals' wild cousins or ancestors. Many, though, are shared by humans: smaller bodies, thinner bones, shorter faces, smaller brains, and reduced physical differences between males and females. Judging from the fossil record, these changes in humans started around 200,000 years ago, when Homo sapiens came into existence.

Why did these changes happen? For an evolutionary biologist, that question is normally equivalent to asking: what adaptive purpose did they serve? In this case, however, the answer is unusual: none. A decades-long, painstaking experiment by two Russian geneticists working in Siberia showed that reduced brain size, thinner bones, white spots, and all the other marks of the domestication syndrome are incidental byproducts of the biochemical processes that carry out the primary adaptation: reduced reactive aggression.

The body's main mechanism for reducing reactive aggression is neural-crest cell migration. To simplify: neural-crest cells are a special kind of cell that carries developmental instructions throughout the embryo and fetus. In organisms selecting against reactive aggression, neural-crest cell migration is delayed and certain instructions go astray, resulting in white patches, floppy ears, and the rest of the domestication syndrome. Besides these anatomical markers, there are also behavioral and physiological ones having to do with fear response, playfulness, learning rates, sexual behavior, and hormone production, among others. What these anatomical, behavioral, and physiological signs all have in common is paedomorphism (literally, "child shape"). In dogs, foxes, guinea pigs, and many other species, domesticated animals resemble the juvenile stage of the wild animals they descended from. Humans evolved from our Homo ancestor several hundred thousand years ago, and there aren't sufficient fossils to demonstrate paedomorphism directly. But there are plenty of Neanderthal fossils, and comparisons strongly suggest that present-day humans are, in many respects, juvenilized - that is, domesticated - versions of our remote ancestors.

What caused human and non-human communities to select against reactive aggression? For non-humans in the wild, answers are a little sparse. Ant agriculturalists apparently self-domesticated millions of years ago. Bonobos are the best example, with both the causes and the techniques of self-domestication very well-known. In the case of humans, the cause of selection against reactive aggression was probably the fact that group life requires a minimum of stability, and no trait is more disruptive than reactive aggression, which fuels such behaviors as quests for dominance and demands for submission; arrogance, bullying, and random violence; and monopolizing food and females. That is a behavioral profile of the alpha male, the arch-reactive aggressor. Communities must either endure such pests or eliminate them. Once humans could communicate (the origin of language can't be narrowed down further than 300,000 to 500,000 years ago, but empathy or "shared intentionality" appears to be independent of language and might be sufficient for communication), the die was cast. The origin of domestication, Wrangham proposes, was group execution of alpha males. Civilization is founded on capital punishment - or, to give it its anthropological name, "coalitionary proactive aggression,"

The executioners were adult males, usually married. (One of alpha males' most salient offenses was commandeering other men's wives.) Over time, as alpha individuals were regularly killed and the gene for reactive aggression became less frequent in a population, the coalition of executioners became more stable. Their power was, in effect, absolute - anticipating Max Weber's famous definition of the state: "the agency with a recognized monopoly of violence." Staying on the right side of them came to seem a matter of life and death (by execution or - what often amounted to the same thing - ostracism). Community members would have welcomed rules that told them which behaviors were dangerous. They would also have cultivated a reputation for beneficence, since antisocial behavior was the original sin. These developments may have given rise to two of the most distinctive features of human morality: our orientation to abstract standards of right and wrong, and our much greater degree of prosociality - altruism, cooperation, fairness, etc. - than is found in other primates.

By making us reflect on the rightness of our actions and want to be seen as helpful and kind, coalitionary proactive aggression gave birth to virtue. But in replacing the limited power of the alpha male with the unlimited power of the executioners and eventually of the state, "coalitionary proactive aggression is responsible for war, massacre, slavery, ritual sacrifice, torture, lynchings, gang wars, political purges, and similar abuses of power." That is the book's constitutive paradox. Planned, coordinated violence (vernacular for "coalitionary proactive aggression") gave us a social order that made virtue adaptive. But that social order also made exploitation and oppression possible, by the state or by favored or powerful subgroups. We are, Wrangham concludes, "the best and worst of species."

Wrangham is anxious not to be misunderstood. There is apparently a Rousseauist faction among social scientists who reject the idea that any violent tendency is inherited, on the ground that militarists will then dismiss all demands for peace as "against nature" or that male violence against women will be excused as "natural." This is a perennial objection to one or another aspect of evolutionary theory (and most other kinds): it has no business being true, so it isn't. But such objections greatly overestimate the political importance of what we believe about evolution, and indeed of ideology in general. After all, it was not because they believed in the "culture of poverty" theory that neoconservatives opposed the welfare state, but vice versa. It is not because they had a certain view of the Hayek-Keynes debate that Republican lawmakers voted huge tax cuts for the rich in the Reagan, Bush II, and Trump administrations. Efficient markets theory was always an inadequate justification for financial deregulation, but Wall Street wanted deregulation, so any justification would do.

Evolution is more relevant to politics than string theory but much less relevant than moral and historical imagination. "History is far more important than evolutionary theorizing as a reminder about human potential," Wrangham protests. We shouldn't let ourselves off the hook by assuming that human nature makes progress toward equality and peace either impossible or inevitable. It's neither; it's just damned hard.

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George Scialabba's most recent book is Slouching Toward Utopia.