A new study of violent behavior in more than 1,000 mammal species found the meerkat is the mammal most likely to be murdered by one of its own kind.
The study, led by José María Gómez of the University of Grenada in Spain and published Wednesday in the journal Nature, analyzed more than 4 million deaths among 1,024 mammal species and compared them with findings in 600 studies of violence among humans from ancient times until today.
The findings tell us two things:
- Some amount of violence between humans is attributable to our place on the evolutionary tree.
- Meerkats are surprisingly murderous.
To be clear, the study's authors did not set out to prove (or disprove) a theory of meerkat violence; they were investigating what mammalian data might tell us about humans. But Ed Yong at The Atlantic organized the study's exhaustive list of mammals to make this helpful chart ranking animals by their murderousness.
Some of the animals with reputations for docility are actually more dangerous to each other than creatures known for their aggression. Chinchillas kill each other more often than brown bears turn on their own kind. New Zealand sea lions are more murderous than actual lions.
And, as you can see, about 20 percent of meerkat deaths are murders. Their violence has been documented; a 2006 study described in National Geographic documented meerkat mothers killing the offspring of other females to maintain dominance.
In our worst times, humans display murderous behavior; the newly published study found rates of lethal violence between 15 percent and 30 percent for human populations living between 500 and 3,000 years ago.
Today, the rate of lethal violence is much lower. As a companion article published Wednesday in Nature by evolutionary biologist Mark Pagel notes:
"Rates of homicide in modern societies that have police forces, legal systems, prisons and strong cultural attitudes that reject violence are, at less than 1 in 10,000 deaths (or 0.01%), about 200 times lower than the authors' predictions for our state of nature."
So, we are not, as a rule, as lethally violent toward our fellow man as meerkats are toward each other. But the study argues that over all of human history, humans are still more lethally violent than the average mammal.
The authors used the fact that closely related species usually show similar rates of interpersonal violence to predict a 2 percent rate of lethal violence among humans. That means that 2 out of every 100 human deaths would be a murder taking into account only our place on the evolutionary tree, and nothing about political pressures, technology or social norms.
In comparison, among mammals in general just 0.3 percent of deaths are murders. For the common ancestor of primates, the rate is 2.3 percent.
With 2 percent as a human baseline, we come across as both uncommonly peaceful for primates and uncommonly violent for mammals.
One critique of the human part of the paper, with its enormous data sets from 600 previous studies, is that the definition of murderous behaviors is too broad. The authors include infanticide, execution, cannibalism and battlefield deaths in their analysis.
Polly Wiessner, an anthropologist at the University of Utah, told The Atlantic, "They have created a real soup of figures, throwing in individual conflicts with socially organized aggression, ritualized cannibalism, and more. The sources of data used for prehistoric violence are highly variable in reliability. When taken out of context, they are even more so."