Nature or nurture: is violence in our genes?

September 28, 2016
Credit: CC0 Public Domain

Nature or nurture? The quest to understand why humans kill one another has occupied the minds of philosophers, sociologists and psychologists for centuries.

Are we innately violent, as Englishman Thomas Hobbes postulated in the 1650s, or is our behaviour influenced more by the environment we grow up in, as Jean-Jacques Rousseau theorised a century later?

On Tuesday, a team of scientists who looked at the question from a new angle—that of evolutionary biology—concluded that our violent nature was at least partly inherited from an , and shared with other primates.

Lethal violence appears to be "deeply rooted" in the lineage of monkeys, apes and Homo sapiens, the researchers wrote in the science journal Nature.

This, in turn, suggests that "a certain level of lethal violence in humans arises from the occupation of a position within a particularly violent mammalian clade."

A clade is the biological term for a group of organisms descending from a common evolutionary ancestor.

The Spanish researchers gathered data on more than four million deaths in 1,024 present-day mammal species, as well as 600-plus human populations from the late Stone Age some 50,000-10,000 years ago until today.

The animals sampled represent some 80 percent of mammal families.

The researchers looked specifically at the proportion of deaths caused by lethal violence perpetrated by a member of the same species—in humans this was war, homicide, infanticide, execution and other intentional killings.

They also searched for similarities between species with common ancestors, which they used to infer how violent those predecessors would have been, and to reconstruct a history of ancestral killing rates.

Overall, the researchers found, intraspecies killing was the cause of about 0.3 percent of mammal deaths.

Turning it off

But for the ancestor of all primates, rodents and hares, killings caused about 1.1 percent of deaths, rising to 2.3 percent for the next, more recent, common ancestor of primates and tree shrews.

By the time the common human ancestor first appeared around 200,000-160,000 years ago, the rate was about two percent—similar to that for other primates, the team found.

"This means that humans have phylogenetically inherited their propensity for violence," they wrote.

Phylogenetics is the study of the genetic relationship between species over time, giving us the so-called evolutionary tree, with a primordial ancestor at its base from which all organisms developed.

Study co-author Jose Maria Gomez Reyes told AFP the new data showed there was "an evolutionary component to human violence, not that this is the only component."

This evolutionary component are not only genetic, and "most likely" influenced by environmental pressures on survival.

"In fact, social behaviour and territoriality, two behavioural traits shared with relatives of (Homo) sapiens, seem to have also contributed to the level of lethal violence... inherited in humans," said the study.

Commenting on the study, Mark Pagel of the University of Reading said it provided "good grounds for believing that we are intrinsically more violent than the average mammal."

But it also showed that humans are able to curtail such tendencies.

"Rates of homicide in modern societies that have police forces, legal systems, prisons and strong cultural attitudes that reject violence are, at less than one in 10,000 deaths (or 0.01 percent) about 200 times lower than the authors' predictions for our state of nature," he wrote.

"Hobbes has landed a serious blow on Rousseau, but not quite knocked him out."

Explore further: Alcohol-involved homicide victimization—common, linked to male gender, minority status, and history of domestic abuse

More information: Nature, nature.com/articles/doi:10.1038/nature19758

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TheGhostofOtto1923
not rated yet Sep 28, 2016
"Nature or nurture? The quest to understand why humans kill one another has occupied the minds of philosophers, sociologists and psychologists for centuries."

-No wonder we havent gotten very far in understanding it.

"This, in turn, suggests that "a certain level of lethal violence in humans arises from the occupation of a position within a particularly violent mammalian clade."

-Violence is a symptom of overpopulation. Humans systematically conquered their natural attritive elements while their tropical rate remained the same. Chronic competition over resources was the result.

""an evolutionary component to human violence..."

-Humans were continuously selected for their prowess at wresting resources from their human competitors. They did this as cooperating members of tribes. So not only did they become more efficient fighters, they developed better ways of fighting as members of a group.
TheGhostofOtto1923
not rated yet Sep 28, 2016
""Rates of homicide in modern societies that have police forces, legal systems, prisons and strong cultural attitudes that reject violence are, at less than one in 10,000 deaths (or 0.01 percent) about 200 times lower than the authors' predictions for our state of nature," he wrote."

-And these are the societies where the people are living within their means and the growth rate does not exceed the carrying capacity of the region where they reside.

Elsewhere, violence reigns. 'Strong cultural attitudes that reject violence' NEVER survive once populations exceed the limits of stability. Weimar becomes the third reich. Democracy descends into tyranny.

Why cant these people ever acknowledge the roles of overpopulation and tribalism in the human condition? Because it explains too much? Because its too embarrassing? China seemed to have no problem with it-
RobertKarlStonjek
not rated yet Sep 29, 2016
Cont...
Nature and Nurture are only part of the story of behaviour. Neuroscience, for instance, concentrates almost entirely on the present condition (4) using a generic or neutral subject (eg the average of many, so as to control for 1,2 & 3 as far as possible).

The Nature-Nurture only debate takes a knife and attempts to excise half of all the sciences concerned with behaviour...not good...
RobertKarlStonjek
not rated yet Sep 29, 2016
There are four categories for the determinants of behaviour, not two as implied by the article:
1) Genetic predisposition: the genetic and epigenetic contributors to behaviour (the speciality of Evolutionary Psychology)
2) Experience through life: your interaction with the environment, your conditioning (operant and respondent, as researched by behaviourists);
3) Cultural: the collected experience of hundreds of people over many centuries that can condition your behaviour to, or in anticipation of, environment that you have never personally experienced; (Evolutionary Psychology, social psychology etc)
4) The current conditions: the current state of your brain, of your consciousness, of the impact on your senses of your surroundings and so on (as explored by cognitive neuroscience, consciousness studies among others).
sascoflame
not rated yet Sep 29, 2016
Apparently, none of the various luminaries who have studied the issue of violence in humans have heard of the law of evolution. If violence gives an evolutionary advantage to some individuals then it is highly likely to occur.
TheGhostofOtto1923
not rated yet Sep 29, 2016
Apparently, none of the various luminaries who have studied the issue of violence in humans have heard of the law of evolution. If violence gives an evolutionary advantage to some individuals then it is highly likely to occur.
It's not the quantity of violence but the quality of it. Group selection favored tribes that could wage better cooperative violence against their enemies. This required that individuals surrender all sorts of natural prerogatives for the good of the tribe.

One of these was the tendency toward violence in intratribal competition. Tranquility increased within the tribe even as violence increased toward outsiders.

And this is exactly what the major surviving religions dictate. They survive because they were better at outgrowing and overrunning the competition.

They are also the result of group selection.

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