In a study published in Nature this week(1), a group of Spanish researchers explore the origin and evolution of human lethal violence. The conclude that humans inherited a propensity for violence from our primate ancestors.
Although it is not easy to estimate how often animals kill each other in the wild, Gómez and his team compiled sources of mortality for a comprehensive sample of mammals (see figure). They show that 60 percent of mammal species, like pangolins and porcupines, do not seem to kill one another at all, although that figure probably underestimate lethal violence, because information is not available for many species. Bats and whales almost never kill their own kind, whereas the number of hyenas killed by other hyenas is around 8 percent, and as many as 17 percent of deaths in some lemur species result from lethal violence.
Using this phylogenetic information, they predict that the proportion of human deaths caused by interpersonal violence should stand at 2%. This is similar to the murder rate seen in prehistoric bands and ethnic groups, until about 10,000 years ago. This phylogenetic effect entails more than a mere genetic inclination to violence. Social behaviour and territoriality, two traits shared with relatives of H. Sapiens, seems to have also contributed to the level of lethal violence. The level of lethal violence has changed as our history progressed, mostly associated to with changes in the sociopolitical organisation of human populations.
Kudos to Thomas Hobbes!
(1) Gómez, José María, Miguel Verdú, Adela González-Megías, and Marcos Méndez. ‘The Phylogenetic Roots of Human Lethal Violence’. Nature, 28 September 2016. doi:10.1038/nature19758.