Stochastic group selection model for the evolution of altruism
Abstract
We study numerically and analytically a stochastic group selection model in which a population of asexually reproducing individuals, each of which can be either altruist or non-altruist, is subdivided into
M
reproductively isolated groups (demes) of size
N
. The cost associated with being altruistic is modelled by assigning the fitness
1−τ
, with
τ∈[0,1]
, to the altruists and the fitness 1 to the non-altruists. In the case that the altruistic disadvantage
τ
is not too large, we show that the finite
M
fluctuations are small and practically do not alter the deterministic results obtained for
M→∞
. However, for large
τ
these fluctuations greatly increase the instability of the altruistic demes to mutations. These results may be relevant to the dynamics of parasite-host systems and, in particular, to explain the importance of mutation in the evolution of parasite virulence.