prediction turns out to be true. The citizens of countries with more of a long-term orientation commit fewer homicides, as do the citizens of countries that emphasize restraint over indulgence.127
So the theory of the Civilizing Process, like the theory of the expanding circle, has found support in experiments and datasets that are far from its field of origin. Psychology, neuroscience, and economics have confirmed Elias’s speculation that humans are equipped with a faculty of self-control that regulates both violent and nonviolent impulses, that can be strengthened and generalized over the lifetime of an individual, and that can vary in strength across societies and historical periods.
So far I have not mentioned yet another explanation for the long-term growth of self-control: that it is a process of evolution in the biologist’s sense. Before turning to the last two of our better angels, morality and reason, I need to spend a few pages on this vexed question.
RECENT BIOLOGICAL EVOLUTION?
Many people casually use the word evolution to refer both to cultural change (that is, history) and to biological change (that is, a shift in the frequencies of genes across generations). Cultural and biological evolution can certainly interact. For instance, when tribes in Europe and Africa adopted the practice of keeping livestock for milk, they evolved genetic changes that allowed them to digest lactose in adulthood.128 But the two processes are different. They can always be distinguished, in theory, by experiments in which babies from one society are given up for adoption and brought up in another. If biological evolution has taken place in response to the distinctive culture of either society, then the adopted children should differ, on average, from their native peers.
A frequently asked question about declines in violence is whether they can be attributed to recent biological evolution. In a society that has undergone a Pacification or Civilizing Process, has the genetic makeup of the people changed in response, helping the process along and leaving them permanently less disposed to violence? Any such change would not, of course, be a Lamarckian absorption of the cultural trend into the genome, but a Darwinian response to the altered contingencies of survival and reproduction. The individuals who happen to be genetically suited to the changed culture would outreproduce their neighbors and contribute a larger share of genes to the next generation, gradually shifting the population’s genetic makeup.
One can imagine, for example, that in a society that was undergoing a Pacification or Civilizing Process, a tendency toward impulsive violence would begin to pay off less than it did in the days of Hobbesian anarchy, because a hair trigger for retaliation would now be harmful rather than helpful. The psychopaths and hotheads would be weeded out by the Leviathan and sent to the dungeons or gallows, while the empathizers and cooler heads would bring up their children in peace. Genes that fortified empathy and self-control would proliferate, while genes that gave free rein to predation, dominance, and revenge would ebb.
Even a cultural change as simple as a shift from polygyny to monogamy could, in theory, alter the selective landscape. Napoleon Chagnon documented that among the Yanomamö, the men who had killed another man had more wives and more children than the men who had never killed; similar patterns have been found in other tribes, such as the Jivaro (Shuar) of Ecuador.129 This arithmetic, if it persisted over many generations, would favor a genetic tendency to be willing and able to kill. A society that has shifted to monogamy, in contrast, removes this reproductive jackpot, and conceivably could relax the selection for bellicosity.
Throughout this book I have assumed that human nature, in the sense of the cognitive and emotional inventory of our species, has been constant over the ten-thousand-year window in which declines of violence are visible, and that all differences in behavior among societies have strictly environmental causes. That is a standard assumption in evolutionary psychology, based on the fact that the few centuries and millennia in which societies have separated and changed are a small fraction of the period in which our species has been in existence.130 Since most adaptive evolutionary change is gradual, the bulk of our biological adaptation must be to the foraging lifestyle that prevailed during those tens of millennia, rather than to the specifics of societies that have departed from that lifestyle and diverged from each other only recently. The assumption is supported by evidence for the psychic unity of humankind—that people in every society have all the basic human faculties such