As a species, humans seem to have inherited murderous traits via evolution and genetics, but civilization has tamed some of it out, a new study suggests.
Scientists in Spain calculated the rate at which over a thousand mammal species kill their own kind, and observed that closely related species have parallel violent tendencies. They found that where a specis if on the evolutionary tree says a lot about how savage it can be towards its own kind.
Humans, as it turns out, are “in a position within a particularly violent mammalian clade, in which violence seems to have been ancestrally present.” This means that based on the species closely related to humans, the “propensity for violence” is inherited, CBS News reports.
Mammals as a group average around three murders in 1,000 deaths.
The “root” violence rate of the earliest humans and primate cousins is around 20 in 1,000. In the medieval period, from 700 to 1500 AD, that number went up drastically to 120 per 1,000 deaths, according to lead study author Jose Maria Gomez.
But over time, humans have gotten less savage.
The modern-day average for murder among humans is at 13 in 1,000, Gomez says, using World Health Organization data as the basis. But the exact numbers are difficult to calculate, with many variables to consider, so Gomez says it’s more accurate to say that “violence has decreased significantly in the contemporary age.”
Surprisingly, the most peaceful mammals are killer whales. Despite the name, they have a violence rate of nearly zero among their own, along with other whale species, bats and anteaters. Cougars, some baboon species, lemurs and chinchillas are among the most violent, with murder rates well above 100 in 1,000.
Gomez’s study took a look at violence through a unique perspective – that of phylogenetics, the study of how closely related species appear to share similar traits. As the researchers found, the more closely related the species are, the more comparable the violence levels.
The researchers examined 1,044 studies that analyzed 1,024 mammal species, with the causes of death confirmed for over 4 million individual mammals. As the scientists moved up the evolutionary chain, they found that a superorder of species called Euarchontogilires, which includes early humans, rodents and hares, has a violence rate of 11 in 1,000. Further down history, a large grouping called Euarchonta that again includes humans, primates, flying lemurs and tree shrews showed a violence rate of 23 in 1,000.
Gomez examined several thousand prehistoric human deaths across archeological sites all over the world, and admitted that it was difficult to calculate violence rates for this time.
The researchers concluded that culture, government, modernization and other factors have since reigned in the inherent violence humans have. They do state that “the level of lethal violence is reversible and can increase or decrease as a consequence of some ecological, social or cultural factors.”
The study, which also found meerkats to be the most murderous mammals, was published in the journal Nature.
