Scientists battle over whether violence has declined over time

Contrary to a popular idea among researchers, modern states haven’t dulled people’s long-standing taste for killing each other in battle, a controversial new study concludes. But living in a heavily populated society may up one’s odds of surviving a war, two anthropologists propose.

As a population grows, larger numbers of combatants die in wars, but those slain represent a smaller average percentage of the total population, say Dean Falk of Florida State University in Tallahassee and Charles Hildebolt of Washington University School of Medicine in St. Louis. That pattern holds for both small-scale and state societies, the researchers report online October 13 in Current Anthropology.

Increasing absolute numbers of war dead in human societies have resulted from the invention of ever-more-lethal weapons, from stone axes to airborne bombers, the researchers suspect. But Falk and Hildebolt show that states, which centralize political power in a bureaucratic government, are less likely to lose large portions of their populations to war than are small-scale societies, such as hunter-gatherers. That’s a consequence of large populations acting as a buffer against war casualties among noncombatants, not a lesser appetite for violence, the researchers contend.

“Small-scale societies are not more violent than states,” Falk says. “But there is safety in numbers.”

Falk says the new findings challenge the idea that, starting around 5,000 years ago, states reduced rates of violence and war deaths characteristic of earlier, much smaller human groups (SN: 8/10/13, p. 10). Harvard University psychologist Steven Pinker argued in a 2011 book, The Better Angels of Our Natures, that states reversed the tide of violence in several ways, including the formation of trade networks and the suppression of raids and feuds.

Pinker calculated an annual average death rate from warfare in 27 recent nonstate societies as 524 per 100,000, about half of 1 percent. States ranging from the Aztec empire to 20th century Russia and the United States had rates no more than about half as large as that, even with two world wars.

Falk and Hildebolt’s data don’t support a blanket argument for safety in numbers, Pinker says. “For an average person, life was far more dangerous in nonstate societies.”

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In the new study, Falk and Hildebolt analyzed previously collected data on population sizes and deaths from intergroup conflicts in 11 wild chimpanzee communities, 24 human nonstate societies, 19 countries that fought in World War I and 22 countries that fought in World War II. Data from the two world wars included only military deaths. Each world war included states of varying population sizes and represented many millions of military deaths, making the two conflicts good platforms for studying the effects of population size on war deaths, the researchers contend. The study also included data from 97 wars between states that occurred from 1820 to 1997. Average annual death rates as a percentage of the total population were calculated for societies in each war.

On average, chimps were not as violent as humans. Still, as in human societies, average annual deaths from conflicts in chimp communities declined as populations increased.

The researchers didn’t examine whether, in human societies, average annual death rates from causes other than warfare, such as murder and terrorism, show any relationship to population sizes. But Falk suspects a “safety in numbers” pattern holds for violent acts outside warfare. 

Pinker disagrees, asserting that many nonstate societies have suffered higher rates of violent deaths than states have, even during the latter nations’ especially bloody world wars. Calculating average annual death rates for nonstate societies obscures the fact that death rates in eight of those societies included in the new study ranged from around 4 to 8 percent, compared with rates of no more than about 2.5 percent for World War I countries and no more than about 1.5 percent for World War II countries, Pinker says.

Population sizes also can’t explain dramatic differences in death rates among countries that participated in the two world wars, Pinker adds. For instance, a nearly 1 percent average annual death rate for the Soviet Union during World War II versus near zero for India had more to do with India lying thousands of miles away from major theaters of war than population sizes, he argues.

Falk and Hildebolt show that average rates of battle deaths indeed tend to fall as populations become larger, says Harvard biological anthropologist Richard Wrangham. But he agrees with Pinker that many nonstate societies have been more violent than states.

Much of the decline in violence in early states involved reduced numbers of murders and blood feuds, fostered by government rule and law enforcement, says political scientist Azar Gat of Tel Aviv University. States waged wars by conscripting a small percentage of the population into armies that often fought far from where civilians lived, thus lowering war fatalities, Gat says.

Over the last two centuries, peaceful economic competition among industrialized nations has further reduced war’s frequency and lethality, Gat holds.