Humans ‘inherit’ murderous trait through evolution - study

© Philippe Wojazer
Evolution predisposes humans to murder, according to a study which examined how often a range of mammals kill members of the same species.

The study, carried out by four Spanish institutions and published in Nature, reveals that instances of lethal violence among mammals are quite rare and are spread across a wide range of species, occurring in almost 40 percent of the 1,024 mammal species studied.

The team used statistical models to estimate the likely murder rate amongst mammal’s evolutionary ancestors at various points in their family tree, finding that lethal violence is more common in some species than others. It’s particularly frequent among mammals with social tendencies.

The list throws up a number of interesting results: New Zealand sea lions kill each other more often than actual lions and blue monkeys are nearly twice as murderous as brown bears.

Top of the pile when it comes to murderousness, though, is the meerkat. The animal is famed for group cooperation but murder accounts for around one in every five meerkat deaths.

Murder was the cause of around 2 percent of deaths among the first humans - more than six times higher than average amongst mammals in general. For the common ancestor of primates, the rate was 2.3 percent.

Rates of lethal violence among humans has risen and fallen over the centuries. During Palaeolithic times the rate rose, accounting for nearly 4 percent of all deaths. During Medieval times, between 400 and 1400 AD, that figure soared to around 12 percent. Today, the rate is much lower, as evolutionary biologist Mark Pagel notes in a companion article which was also published in Nature.

The authors of the mammalian lethal violence study attribute the drop to the evolution of human society. "Deadly violence in humans is therefore an undeniable evolutionary component that precedes our own origin as a species,"said Adela Gonzalez Megías, the study’s co-author.

"We found that human lethal violence has an evolutionary origin but can be modulated by some ecological and cultural factors, like the type of socio-political organisation," lead researcher José María Gómez told ResearchGate.

“What it’s saying, in the broadest terms, is that humans have evolved strategies for solving problems with violence,” Pagel toldThe Guardian.

The authors included infanticide, execution, cannibalism and war in their analysis. This broad definition of murderous behavior has drawn some criticism from other researchers.

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."