Thursday, June 1, 2017
Reciprocal Altruism as the Foundation of Group Selection
This is an elaboration of the second point I wish to make in my paper at the APSA this fall. As I stated in my previous post, to make group selection work you need mechanisms that enable altruists to benefit each other and to avoid being exploited. Otherwise, altruists who work to benefit the group at their own expense will promote the reproductive success of cheaters within the group. Since the cheaters pay none of the costs of benefiting the group, they will proliferate at the expense of the altruists. I argue here that another evolutionary vector for cooperative behavior can help to explain how this problem was solved.
Reciprocal altruism is one of the basic explanations for cooperative behavior among organisms. Altruism is here defined in terms of a sacrifice and a benefit, both measured in the coin of the probability of reproductive success. When organism A delivers some benefit to some other organism B, at some cost to A, because it is likely that the favor will be returned, that is reciprocal altruism. I use the term because to indicate the selection pressure that sustains the trait in both organisms.
A paradigmatic example is blood sharing among vampire bats. These nocturnal hunters must feed every three days to survive, leaving them at the mercy of chance as the herds of animals they prey on move around. The bats manage the risk by a system of sharing. If one comes back hungry, she will cozy up to another who obviously sports a full belly. The latter will share some of her bounty because this makes it more likely that the beneficiary will share later. There are many such examples in nature, but almost all of them involves exchanges between individuals.
Christopher Boehm has argued in two magnificent books (Hierarchy in the Forest and Moral Origins) that human social evolution was driven by a specific problem. Human beings have always been extraordinarily good at cooperating with their fellows. This, more than anything, explains why we have inherited the earth. Once we began to cooperate in hunting, gathering, etc., a problem presented. Some members of each group (free riders) were tempted to let everyone else shoulder the burden (pay the cost in reproductive fitness) while taking their share of the bounty. Another kind of problem is the individual who, due to physical and perhaps psychological advantage, was tempted to take more than his share of whatever was of value. If these problems could not be solved, the evolutionary emergence of cooperation would have been precluded. The free riders and bullies would have proliferated in the populations and the cooperators would have withered until the social unit dissolved.
The way that this problem was managed was group enforcement. Cheaters were sanctioned by their comrades. Slackers could easily be marginalized. Bullies required more strenuous interventions; however, even the biggest primate cannot stand up to the crowd and anyway, he is vulnerable while he is sleeping. Boehm proposes that group enforcement eventually became psychologically internalized and that this is the evolutionary origin of the moral sense in human beings.
It occurs to me that this account is a special case of reciprocal altruism. What is special about it is that the parties are not two individuals, as in the paradigmatic cases, but the individual and the group. The individual sacrifices the temptation to take more than his fair share. If someone always has a bum leg when it is time for hunting or war he conserves his energy and avoids risks, the better to invest them in reproductive success. If he tries to push his weight around, again, he is exploiting the group. Every good citizen sacrifices such advantages to the political whole. The group in turn has to pay the costs of enforcement, which may not be negligible if the bully is really big and the slackers are more than a few. If the group is successful, it becomes a powerful cooperative unit.
The social contract has long been regarded as an abstract and artificial invention of philosophers. To the contrary, it seems to be an emergent product of human evolutionary history. I think that there are only two possible ways to make group selection work. One is if the groups frequently break up and reassemble. Those groups with more cooperators than not out compete those that chance to be pregnant with cheaters. I suspect that such a process, continually repeated, might result in the proliferation of altruists.
I suspect, however, that every genuine case of group selection requires enforcement mechanisms. Cheating must be suppressed if cooperation is to flourish. This is true even if the cooperators are mostly related. There are always black sheep in the family. The evolution of politics is proof that the problem of group selection can be solved.