The selfless warrior: When the individual sacrifices himself for the collective.

By: Eduardo Araia

The son of a Vulcan father and an Earth mother, the big-eared Mr. Spock from the Star Trek television series makes his presence felt on screen through an inseparable attachment to logic, a characteristic of his paternal compatriots. But, from time to time, the typically human feelings of his mother's side overcome his Vulcan armor, to the delight of viewers. One of these occasions, at the end of the second film, The Wrath of Khan, could not make Spock's human condition more evident: he sacrifices himself to save all the occupants of the Enterprise.

To give one's life for the survival of the group.

The altruism displayed by Spock and so many other heroes who, of their own free will, give their lives for the survival of the group has always been a subject of discussion among evolutionary biologists and other scientists. Is this characteristic definitively incorporated into our genes through the evolutionary process defended by Charles Darwin? The subject has been studied for decades, and the initial conclusion was that acts of supreme personal sacrifice could not be explained by natural selection – except those related to the prospect of helping the survival of close relatives, whose genes are similar to those of the favored individuals.

But Darwin himself had already suggested a different interpretation of the subject in his book *The Descent of Man*, from 1871. The frequent struggles between prehistoric tribes could have contributed to fixing this aspect in our genetic heritage. The idea, taken up and expanded in recent years by economics professor Samuel Bowles of the Santa Fe Institute in New Mexico (United States), has stirred the scientific community. For Bowles, altruism may have evolved directly as a consequence of tribal wars in which individual sacrifices were a crucial element for members of a group to defeat their opponents.

From hunters to farmers

"Biologists and economists doubted that a genetic predisposition to behave altruistically – helping others at the cost of one's own life – could evolve, except for extended assistance to genetically close relatives," the researcher observes. The theory he developed contradicts this, proposing that natural selection worked on groups of people who cooperated together, rather than individuals considered in isolation.

According to Bowles, for most of the approximately 200 years of human history, our ancestors belonged to hunter-gatherer tribes – agriculture, which definitively changed this landscape, emerged less than 10 years ago. The daily life of this long period, he observes, implied a practically continuous state of belligerence between tribes. "War was common and deadly enough among our ancestors to favor the evolution of what I call parochial altruism, a predisposition to be cooperative towards members of the same group and hostile towards outsiders," he states.

In general, the idea displeased most biologists because, according to them, these groups did not have sufficient genetic differences to favor group selection (a form of natural selection that assumes differential survival between distinct groups of organisms, thanks to the characteristics present in each group). However, observation in nature and experiments (some of which were carried out by Bowles and his team) showed that altruism is quite common among humans – much more so than in other animal species, in fact. With this, the researcher delved deeper into the subject.

Sharing food

In a 2006 article published in the journal Science, Bowles proposed a mathematical model of this process and revealed that the genetic differences between prehistoric and modern hunter-gatherers were much greater than previously thought – an endorsement of the hypothesis that group selection could have been a powerful evolutionary force. This hypothesis also finds support, for example, in the egalitarian practices among human ancestors (the sharing of food, for instance), which reduced the strength of individual selection against altruistic ones, and in the fact that frequent wars made altruistic cooperation among group members essential for their survival.

When using the word "war" in the context of that era, Bowles emphasizes that he is not referring to large-scale conflicts. "We're talking about groups of men who went out in pairs, trios, or quintets," he says. "They didn't have a chain of command, and it's difficult to see how they could force other people to fight." That's why the altruistic intention on the part of these men was crucial, the researcher points out. Each of them could perfectly well have stayed home instead of risking their lives fighting with rival tribes – but even so, they faced the challenge.

In a study on the subject published in 2009 in Science, Bowles decided to investigate what might have happened to a tribe of altruistic individuals driven to fight other, more selfish tribes. He gathered and analyzed archaeological evidence from Stone Age sites and ethnographic studies of modern hunter-gatherer tribes. According to his conclusions, conflicts between groups were responsible for about 14% of all deaths recorded in early hunter-gatherer societies.

In the end, altruism prevailed.

Next, he estimated the rate at which altruism would reduce an individual's chances of reproducing. Then, he applied the numbers obtained to a model of intergroup competition in which a person's altruism would increase a group's chances of winning the battles. Result: groups with non-selfish individuals were predominant, and within them, altruism prevailed.

Bowles identified two conditions – a sufficiently intense state of belligerence between rival tribes and sufficient genetic differences within these human groups – which, if met, would allow altruism to evolve through the mechanisms proposed by Darwin. In his study, he showed that this did indeed occur: the genetic differences observed within these groups were in fact greater than previously thought, and conflicts were so routine as to shape social behavior at that time. The consequence of this, he concludes, was the occurrence of altruistic acts of personal sacrifice that helped one group survive against another. In other words, the daily situation of war helped these ancestors reduce their degree of selfishness, instilling in them notions of altruism that contributed to the preservation of the groups.

The researcher warns that this "altruistic warrior" theory is only one scenario capable of explaining how altruism evolved in primitive societies. "The willingness to take mortal risks as a combatant is not the only form of altruism (...) more altruistic and therefore more cooperative groups can be more productive and support stronger, healthier or more numerous members, for example, or make more effective use of information," he stressed.