The passage below is accompanied by a set of questions. Choose the best answer to each question.

"Violence is a driver of much of human history," David C. Geary, a cognitive scientist and evolutionary psychologist at the University of Missouri in Columbia, stated in an email. "All of humanity's early empires were built through intimidation and violence." "There's also evidence of aggression before recorded history: bones with evidence of violent death, like embedded arrow points or skulls staved in," says Pat Barclay, an evolutionary psychologist at the University of Guelph in Ontario. That suggests violence predated complex societies and the rise of civilization.

But on the flip side, rates of violence vary (and have historically varied) wildly across cultures and communities, Barclay said. That suggests violence can be dialled up or down dramatically in our species. Nomadic peoples, for example, tend to have lower levels of lethal interpersonal human violence, while eras filled with societies bent on plunder and conquest, unsurprisingly, had higher levels. And modern-day American culture is more violent than most of those in Europe. "There's wide variation in violence rates — order of magnitude difference," Barclay noted. "In some specific recorded societies, up to half of all men die violently at the hands of other men. In other societies, physical violence is very rare, like in modern Japan."

Violence tends to breed violence, meaning that cultures where conflict is common are more likely to experience violence generation after generation, Geary said. In this way, violence is "transmitted" as a contagious disease would be, according to University of Illinois epidemiologist Gary Slutkin. However, Brad Evans, a professor of political violence at the University of Bath in the U.K., pointed out that even people in the most progressive and peaceful communities are capable of violence. "Ordinary, lawful persons can quickly turn into monsters once conditions change; equally, some who are most dislikeable can end up showing remarkable acts of kindness. There is no clear formula as to why a person acts in a violent way. And that is why it is such a complex problem," Evans said.

Additionally, according to both Barclay and Evans, it can be far easier to carry out violent acts if the individual committing the violence is distant from their victims; it is far easier to press a button launching a nuclear missile than it is to physically and directly strike a killing blow. For instance, in Stanley Milgram's classic studies of obedience, in which an experimenter told participants to deliver electric shocks of increasing intensity to other people, participants were more reluctant to shock victims if they were physically closer to them, Barclay noted. And historically, acts of genocide occur after perpetrators dehumanize, or create psychological distance, between themselves and those of a different race or ethnicity.