The application of capital punishment against violent individuals has had a profound genetic impact on human evolution and facilitated the appearance of some features that differentiate the Homo sapiens of other animals, as proposed by the prestigious British primatologist Richard Wrangham, who warns that this hypothesis should not be used to justify its application today.
Compared to chimpanzees, our close cousins with whom we share 99.4% of DNA, human beings are more peaceful. This is because during the last 300,000 years small populations of Homo sapiens they organized themselves to eliminate those individuals who showed violent behavior that endangered the peace and survival of the tribe.
The application of the death penalty, which has been documented in tribes of hunters and gatherers around the world, diminished the likelihood with which genes responsible for aggressive tendencies were passed on to the next generation, says the Professor at Harvard University (USA) in an interview with EL PAÍS held in London. Through that mechanism, he argues, humans self-tamed.
The development of the language favored that individuals who were under the subordination of a despot could forge plans in a safe way to protect themselves from the bully, who was often physically powerful and could have defeated any member of the clan in a direct confrontation.
It is easy to think that we are a violent species. But when you compare the frequency of incidents between humans with that of chimpanzees, you realize that we are much more peaceful
Purging the most belligerent individuals "was a dramatic change in the human evolutionary pressure that provoked a selection against reactive aggressive behaviors, favored peace and tolerance and allowed the emergence of a new type of society," explains Wrangham.
"In newspapers you will always find news from people who have used this type of reactive behavior, so it is easy to think that we are a violent species. But when you compare the frequency of human-to-human incidents with chimpanzees, you realize that we are far more peaceful. This allows us to cooperate in wonderful ways, because we are more tolerant towards the other members of the group to which we belong, "he says.
The decrease in aggression was also associated with anatomical changes. The size of the bones and teeth was reduced, the face narrowed and the differences between the skulls of men and women became smaller. Similar changes have been observed in artificially selected animals for generations to be less aggressive, such as foxes, cats and horses. Also in species that split off from others after thousands of years of domestication, as dogs did of wolves. In all these cases, characteristic features appear that did not occur in their ancestors, such as white spots on the coat and hanging ears.
"All these changes have been a mystery to biologists for a long time," says Wrangham, who was part of the team of primatologist Jane Goodall in the seventies and believes that such processes of self-domestication has occurred in other animal species.
The clearest case is that of the bonobos with respect to the chimpanzees, two species whose behavior Wrangham has studied closely in Tanzania and Uganda. There he realized that the chimpanzees were extremely violent to each other, even killing the offspring of their own group in fits of rage. That shocked with the peaceful and sociable behavior of the bonobos, a species whose genome only differs by 0.4% from that of chimpanzees.
The British researcher concluded that the bonobos have evolved in ways that entail a reduction in their aggressiveness, although with a different mechanism than the capital punishment of humans.
Unlike chimpanzees, bonobos evolved in a food-rich area with few competitors, which allowed the females to feed together most of the day. This union allowed them to weather the violent attacks of the dominant males, who found that a less aggressive attitude increased their chances of copulation.
"Bonobos are a domesticated version of chimpanzees," says Wrangham. "That led me to think of humans as a domesticated version of their ancestors."
Much of the anatomical differences between 'Homo sapiens' and two of their already extinct peers, Neandertals and Denisovans, could be attributed to this process of domestication, says the biologist. "The prediction is that we differentiate ourselves from these species in a similar way that the dogs did from the wolves."
Despite the fact that capital punishment played a key role in our evolutionary past, Wrangham warns that the biological analysis of human evolution "has no relevance to the current political debate on the death penalty."