LJKProbability & Statistics Seminar

On Thursday October 24 2013 at 14h00 in Salle 1  Tour IRMA

Seminary of Bahram HOUCHMANDZADEH (UJF, Laboratoire interdisciplinaire de Physique (LIPhy))

Title : Selection for altruism through random drift in variable size populations

Summary

Altruistic behavior is defined as helping others at a cost to oneself and a lowered fitness. The lower fitness implies that altruists should be selected against, which is in contradiction
with their widespread presence is nature. Present models of selection for altruism (kin or multilevel) show that altruistic behaviors can have ’hidden’ advantages if the ’common good’ produced by altruists is restricted to some related or unrelated groups. These models are mostly deterministic, or assume a frequency dependent fitness.
Evolutionary dynamics is a competition between deterministic selection pressure and stochastic events due to random sampling from one generation to the next. We show here that an altruistic allele extending the carrying capacity of the habitat can win by increasing the random drift of “selfish” alleles. In other terms, the fixation probability of altruistic genes can be higher than
those of a selfish ones, even though altruists have a smaller fitness. Moreover when populations
are geographically structured, the altruists advantage can be highly amplified and the fixation
probability of selfish genes can tend toward zero. The above results are obtained both by numerical
and analytical calculations. Analytical results are obtained in the limit of large populations.
The theory we present does not involve kin or multilevel selection, but is based on the existence of random drift in variable size populations. The model is a generalization of the
original FisherWright and Moran models where the carrying capacity depends on the number of altruists.
