Individual selection or group selection? More reasonably, how about multilevel selection?
Is evolution driven entirely by selection at the level of the gene, by competition between individuals?
Or is evolution also driven in appropriate circumstances by selection at the level of the society (family to empire), by competition between groups?
If we shouldn’t, or can’t, explain all of our social behaviours as being solely aspects of culture, if social selection occurs in nature as well as in theory, shouldn’t there be empirical evidence of its operation? Specifically, shouldn’t we be able to point to examples of multlevel selection?
In a modest way, a modest study reported last week presents one such example.
On July 4th, Science Daily published “How Cooperation Can Trump Competition in Monkeys.”
The study, initially published in the Proceedings of the Royal Society, collected data on gelada monkeys (also known as gelada baboons) during a five-year period ending in January 2011, reports the primary discovery that “being the top dog — or, in this case, the top gelada monkey — is even better if the alpha male is willing to concede at times to subordinates.”
Alpha male geladas who allowed subordinate competitors into their group had a longer tenure as leader, resulting in an average of three more offspring each during their lifetimes.
The report indicates that “while it is not yet clear that a willing exchange is occurring — subordinate males may simply steal some chances at reproduction — the evidence is strong that subordinates confer some benefit to the leader.”
The primary benefit for the alpha male was the support that his subordinate males provided for the defense of the group’s females. With this extra muscle, dominant males were able to hold their status longer than did the alphas in groups without subordinate, breeding males.
Cooperation can evolve among competitors through a variety of mechanisms. In the study, researchers chronicled how it can evolve in the context of reproductive sharing.
Some will argue that the study shows nothing about group selection and shows only how cultural change — in this case, alteration of the composition of a group’s hierarchy — complements and influences individual selection. If you’re convinced that there is no such thing as group selection, then you won’t see group selection. Evidence that could be taken to support group selection will be seen, rather, as something else. “That wasn’t a chipmunk. We don’t have chipmunks here. You must have seen a small squirrel with a damaged tail.” That sort of thing. We all do it, and more often than we like to admit.
If you’re open to the possibility of multilevel selection, you can look at the present study in a very different way. In multilevel selection, individuals compete with each other for dominance within their groups. At the same time, the group competes cooperatively against other groups. The potential interactions between the two kinds of selection are many, and complex.
Does the advantage that a cooperating individual gains generate pressure to cooperate, in which case individual selection drives group selection, since these groups outcompete other groups when it comes to stability and safety? Or does the inclination to cooperate generate advantage for the alpha individual, in which case group selection drives individual selection, since the alphas of cooperative groups thrive compared to the alphas of non-cooperative groups. The answer could be one or the other, or, more likely, some fluctuating dance of one then the other, the other then the one.
Viewed this way, the study could then be seen as supporting, in its small way, the theory of multilevel selection.