Wednesday, July 12, 2006

Group (multilevel) selection: don't call it a comeback

Evolution of cooperation by multilevel selection

Arne Traulsen and Martin A. Nowak

PNAS July 18, 2006, vol 103, 10952-10955

We propose a minimalist stochastic model of multilevel (or group) selection. A population is subdivided into groups. Individuals interact with other members of the group in an evolutionary game that determines their fitness. Individuals reproduce, and offspring are added to the same group. If a group reaches a certain size, it can split into two. Faster reproducing individuals lead to larger groups that split more often. In our model, higher-level selection emerges as a byproduct of individual reproduction and population structure. We derive a fundamental condition for the evolution of cooperation by group selection: if b/c > 1 + n/m, then group selection favors cooperation. The parameters b and c denote the benefit and cost of the altruistic act, whereas n and m denote the maximum group size and the number of groups. The model can be extended to more than two levels of selection and to include migration.

a notable excerpt:
In our opinion, group selection is an important organizing principle that permeates evolutionary processes from the emergence of the first cells to eusociality and the economics of nations.

The authors mention the complications that may arise from the fact that kin selection is also operating in real groups of organisms.

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