Do people kill each other because it’s in our blood, or is it all based on our environment? Philosophers and scientists have exchanged theories for centuries. But an extensive climb through the mammalian evolutionary tree brought scientists to a new vantage point. From there, the answer seems to be a mix of both, but mostly it’s in our blood.
After painstakingly compiling more than 4 million murder records across 1,024 mammal species, evolutionary biologists at the University of Granada found that humans are more vicious than most mammals, but generally similar to our primate lineage. And this fits well with the rest of the evolutionary tree, in which species tended to group together as murderous, somewhat savage, or peaceful. Being territorial and social were big determinants of those bloodthirsty gangs, the authors note. All in all, the finding, published this week in Nature, provides solid support for the argument that killing drive stems from evolutionary roots.
However, when the researchers measured the murder rates of human populations from 50,000 B.C. And the time span for those fluctuations in ferocity is too rapid for a genetic explanation. Societies, it seems, can change our killer instincts.
However, not everyone fully buys the analysis on humans. “The material we have on prehistory is very thin,” Polly Wiessner, an anthropologist at the University of Utah in Salt Lake City, told me. Science. She noted that the study’s authors weighed records such as modern kill rates evenly with more error-prone missionary accounts and ancient battlefield excavations.
Another sticking point is that the authors have thrown all the murders together. But not all murders are created equal, argues Harvard biological anthropologist Richard Wrangham. “In primates, infanticide is undoubtedly the most common form,” Wrangham said The Atlantic Ocean. But humans are “killing adults at an exceptionally high rate…. That’s worth emphasizing to avoid readers jumping to the conclusion that there’s nothing surprising about human violence. People are truly exceptional.”
The study’s lead author, José Maria Gómez, agreed with the criticism, explaining that there simply wasn’t enough data to tell the types of homicides apart.
Still, the mammal-wide comparison of homicide rates is impressively curated and interesting, Wiessner said. According to the study, the overall mammalian homicide rate is only about 0.3 percent (that’s one homicide in every 300 deaths). For about 60 percent of mammals, there was no data on lethal force at all. In general, “species that we would expect to be violent, such as the predatory carnivores, are violent, and species that we would not expect to be violent because they are primarily vegetarian tend not to be,” evolutionary biologist Mark Pagel wrote in a commentary. . But there were some surprises; the most barbaric of all mammals are found to be meerkats, with a murder rate of about 19 percent.
For us humans, the authors predicted a two percent murder rate at the origin of our species. That’s consistent with our primate ancestors. For example, the researchers calculated that the ancestor of the great apes had a murder rate of about 1.8 percent. From the analysis of humans from 50,000 BC. The authors reported that hunter-gatherers maintained that 2 percent murder rate. However, as people organized into warring gangs, tribes, and states, it shot up to as much as 30 percent (with a lot of uncertainty in that estimate).
Our cruelty has since disappeared. “The homicide rate in modern societies with police forces, justice systems, prisons, and strong cultural attitudes that reject violence is about 200 times lower than the authors’ predictions for our world, at less than 1 in 10,000 deaths (or 0.01 percent). stands. of nature,” Pagel remarked. So the argument that our environment controls our violent ways has not yet been dismissed.
Nature2016. DOI: 10.1038/nature19758 (About DOIs).