To understand why altruistic behavior persists in human societies, the theory of group selection is proposed. Group selection is the hypothesis that natural selection occurs at the group level rather than the individual level, and that altruistic behavior favors the survival of the group. Despite the fact that altruistic behavior is to the detriment of the individual, the transmission of altruistic norms and culture within the group, as well as the institutional arrangements in place, favor the survival of altruistic groups over selfish individuals. The interplay of these factors in human society has allowed altruism to persist and evolve.
In our society, we often see altruistic behaviors like donating blood or cleaning up alleys. But from a natural selection perspective, it’s a bit of a conundrum. This is because altruistic people help others at their own expense, while selfish people can receive help without any effort, and altruistic people are likely to be eliminated in the competition for survival between the two groups. According to natural selection, members of a society will adopt selfish strategies that favor them in the survival competition, so selfishness will eventually become prevalent in our society. However, contrary to this expectation, there is still a lot of altruistic behavior in our society. People suppress their selfishness and act altruistically, despite the fact that they could benefit more from a free ride. Where does this altruism come from?
One of the keys to solving this mystery is the “group selection hypothesis”. Group selection is the hypothesis that just as individual characteristics affect the survival of individuals, so do group characteristics affect the survival of groups. In other words, natural selection acts on groups rather than individuals. Altruistic behavior that would be a weakness under individual selection can become a strength under group selection, giving the group an advantage in the survival competition. For example, consider the Defiler unit in StarCraft, which sacrifices other zerglings to regain energy. If there were many selfish zerglings, no one would be willing to sacrifice, and it would be difficult to win a battle between races. On the other hand, if there are many altruistic Zerglings, they will be willing to sacrifice themselves, and the entire race can win.
If we look at human history, there are points in time when group selection is likely to have come into play. In primitive tribal societies, tribal wars were very frequent and highly lethal. Groups with more altruistic individuals would have been more likely to win these tribal conflicts. Even in hunter-gatherer societies that preceded agricultural societies, hunting and gathering success was highly dependent on how selflessly members cooperated. Over tens of thousands of years of harsh environments, selfless acts of cooperation, such as finding safe shelter and protecting each other from external threats, were essential. The more altruistic a group was, the more likely it was to survive in harsh environments.
However, there are still problems with this hypothesis. In individual selection, altruistic individuals are less likely to succeed than selfish individuals and are at risk of extinction. In group selection, however, a group with many altruistic individuals is more likely to succeed or compete for survival than a group with fewer altruistic individuals. Because individual and collective selection work in opposite directions, the rate of collective selection must be able to overwhelm the rate of individual selection for the theory to be convincing.
Humans have developed “institutions”-rules, customs, and laws that affect the interactions between members of society-that slow down individual selection and amplify the effects of collective selection. One such institution is equal income distribution. The food-sharing practices of ancient hunter-gatherer tribes acted as a mechanism for equalizing income distribution, reducing the difference between altruistic and selfish individuals and thus increasing the likelihood that group selection would occur.
Conformist cultural transmission is another factor that makes group selection stronger. Conforming cultural transmission means that if more than half of the people in a group are altruistic, more people will learn altruistic strategies, leading to more altruistic people, and if more than half of the people are selfish, more selfish people will learn selfish strategies, leading to more selfish people. The reason why adaptive culture transfer is important is that even small differences within a group can make a big difference between groups. For example, suppose you have a group of 55% altruistic people and another group of 45% altruistic people. The difference between the two groups is only 10%, but if conformist culture transfer occurs within the group, the first group will become more and more altruistic, and the second group will become less and less altruistic. This conformist cultural transmission increases the effectiveness of group selection by widening the gap between groups.
So far, we have solved the mystery of how altruistic humans survived by using the theory of group selection. Group selection is the hypothesis that natural selection occurs on a group basis and that group characteristics affect the survival of the group. Humans have maximized the effects of group selection through institutions and conformist cultural transmission, creating an environment where altruistic humans can survive. Although group selection has limitations in that it is not evolutionarily stable, it is a compelling hypothesis that explains how altruistic behavior has evolved in human societies.
