On June 30, 1860, there was a debate in Oxford between Thomas Huxley, Charles 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 grandmother that he claimed descent from an ape. Taking the podium, Huxley thundered that if he had to choose for a grandfather either an ape 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.

The story that Richard Wrangham tells in his new book, “The Goodness Paradox: The Strange Relationship Between Virtue and Violence in Human Evolution,” isn’t quite definitive—it is still a work in progress—but it’s very impressive. Wrangham, a primatologist at Harvard, has spent his career studying the great apes, especially chimpanzees, bonobos, and us. He is perhaps best known for the book “Catching Fire: How Cooking Made Us Human,” published in 2009. In that highly original work, he argued that the discovery, made around 1.9 million years ago, that applying fire to food makes it more palatable transformed human destiny. It did this biochemically, because food contains much more energy when cooked—energy that fuelled a large increase in the size of our brain—and 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,” from 1996, is more continuous with “The Goodness Paradox” than is “Catching Fire.” “Demonic Males” was written in the wake of two momentous discoveries: the violence of chimpanzees and the pacifism of bonobos. The premise of the book is that violence is adaptive, i.e., that it promotes survival. That may not seem controversial now, but it was through much of the twentieth century. Culture was thought to be the source of our antisocial emotions, and any suggestion that they also had biological roots was considered politically retrograde, or at any rate too depressing to contemplate—as though those acting under the influence of inherited tendencies were absolved of all moral responsibility.

Surveying the extensive record of primate violence in “Demonic Males,” Wrangham and Peterson made an intriguing discovery. Infanticide is not uncommon; and adults—usually males—killing other adults of the same species 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, annexation of 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, although “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 physically similar to chimpanzees 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. (Indeed, bonobo society is female-dominated.) Neighboring bonobo communities can mix amicably, which almost never happens among chimpanzees. Sex is much more relaxed and, apparently, enjoyable.

How did this idyllic state of affairs come about? It turns out that 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 that of 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. There are no mountains south of the Congo River, so no gorillas live there, and bonobos 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,” Wrangham and Peterson write.

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,” Wrangham writes. “That discrepancy is the goodness paradox.” Wrangham has been pondering this paradox in the twenty years since the publication of “Demonic Males,” and he 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. The clichés about science being a vast coöperative 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 angry, impulsive, and associated with high levels of testosterone. Proactive aggression is calculating, premeditated, and strategic. Think of those TV Westerns where the hero deliberately provokes a slow-witted, hot-headed 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 is reactively aggressive. Usually, reactive aggression is individual, while proactive aggression is institutional, taking such forms as war or 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, 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. 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 past 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: smaller bodies and brains, thinner bones, shorter faces, and reduced physical differences between males and females. Besides these anatomical markers, there are also behavioral and physiological ones, which involve fear response, playfulness, learning rates, sexual behavior, and hormone production, among others.