In this blog post, we explore why altruism persists in human society even though natural selection favors selfishness. We examine group selection theory and the evolution of cooperation.
In our society, we see many examples of altruistic behavior, such as donating blood or cleaning up the neighborhood. This is not mere coincidence; it plays a crucial role in the maintenance and development of our society. Altruistic behavior fosters trust between individuals and the community, strengthens social bonds, and ultimately helps everyone live in a better environment. However, from the perspective of natural selection, such altruistic behavior is something of a mystery.
Natural selection is a theory that explains the process by which traits advantageous for survival and reproduction are passed on to offspring. If so, since altruistic people help others even at their own expense, while selfish people can receive help without making any effort, altruistic people would inevitably be eliminated in the survival competition between the two groups. According to natural selection, members of society would choose selfish strategies that give them an advantage in the competition for survival, and eventually, selfishness would become rampant in our society. However, contrary to what natural selection predicts, we see plenty of altruistic behavior in our society. Where does the motivation to suppress selfish impulses and act altruistically come from, even when one could maximize benefits by free-riding?
One key to solving this puzzle is the group selection hypothesis. Simply put, group selection is the hypothesis that just as individual traits influence an individual’s survival, group traits influence the survival of the group. In other words, the object of natural selection is not the “individual” but the “group.” What is interesting here is that altruistic behavior, which was a weakness in individual selection, becomes a strength for the group in group selection, giving it an advantage in the struggle for survival.
To better understand this, we need to emphasize the importance of social cooperation once again. Human society has fundamentally developed through mutual cooperation. Since it was difficult to secure all the resources necessary for survival and reproduction through individual ability alone, cooperation was essential. For example, prehistoric humans realized the value of cooperation through large-scale hunting and resource distribution. Such cooperative behavior went beyond being merely a tool for survival; it played a crucial role in forming and maintaining culture and norms.
Consider the Zergling being consumed by a Defiler in the game StarCraft. If there were many selfish Zerglings, none would be willing to die, making it difficult to win battles against other races. On the other hand, if there were many altruistic Zerglings, they would be willing to sacrifice themselves to secure victory for their race.
Looking at human history, there appears to have been significant scope for group selection to operate. In primitive tribal societies, inter-tribal wars were very frequent and had high mortality rates. Groups with many altruistic individuals would have been more likely to prevail in inter-group conflicts. In pre-agricultural hunter-gatherer societies, the success of hunting and gathering depended on how altruistically members cooperated. Altruistic cooperative behaviors—such as finding safe shelter and protecting people from raids—were essential for surviving harsh environments over tens of thousands of years. The more altruistic individuals a group had, the higher its chances of surviving in such harsh conditions.
However, there is still an issue to be resolved. Under individual selection, altruistic individuals cannot be as successful as selfish ones and face the risk of extinction; however, under group selection, groups with many altruistic individuals are more successful or have an advantage in the struggle for survival compared to groups without them. Since individual selection and group selection operate in opposite directions, for the group selection theory to be convincing, it must be proven that the pace of group selection overwhelmed that of individual selection.
Humans have slowed the pace of individual selection and amplified the effects of group selection through “institutions”—such as rules, customs, and laws—that influence interactions among members of society. One such institution is the equitable distribution of income. The food-sharing customs of ancient hunter-gatherer tribes acted as a mechanism for equal income distribution, narrowing the gap between altruistic and selfish individuals and thereby increasing the likelihood of group selection.
Conformist cultural transmission also strongly influenced group selection. Conformist cultural transmission means that if altruistic individuals make up more than half of a group, the number of people willing to adopt altruistic strategies increases, leading to more altruistic individuals; conversely, if selfish individuals make up more than half, the number of people willing to adopt selfish strategies increases, leading to more selfish individuals. Conformist cultural transmission is significant because even minor differences within a group can lead to major differences between groups. Let’s assume there is a group where 55% of individuals are altruistic and another where 45% are altruistic. Although the difference between the two groups is only 10%, if conformist cultural transmission occurs within each group, the number of altruistic individuals in the first group will gradually increase, while in the second group, altruistic individuals will eventually disappear. Conformist cultural transmission widens the gap between groups, thereby significantly amplifying the effects of group selection.
So far, we have used group selection theory to solve the puzzle of how altruistic individuals could survive. Group selection is the hypothesis that natural selection occurs at the group level, with group characteristics influencing the group’s survival. Humans have amplified the effects of group selection through institutions and conformist cultural transmission, thereby creating an environment where altruistic individuals can survive. Although group selection has the limitation of being evolutionarily unstable, it remains a compelling hypothesis that effectively explains how altruistic behavior has evolved in human society.
