  The origin of altruistic behavior, i.e. the behavior that is useful for a
population or a species but goes at the expense of an altruistic individual,
has long been a challenge for students of evolutionary biology. The populations
with altruistic individuals thrive better than those without altruists;
however, the altruists within a population thrive worse than the non-altruists
and their prevalence in the population decreases due to individual selection.
Under certain conditions, the strength of group selection, i.e. the competition
between populations, can surpass the strength of individual selection; however,
such conditions are rarely achieved in practice. It was suggested recently that
chances for altruistic behavior to spread highly increase when it is controlled
not by a single gene but by multiple independent genes substitutable in their
effects on the phenotype of the individual. Here we confirm the original verbal
model published as part of the frozen plasticity theory by numerical modeling
of the spread of altruistic/selfish alleles in a metapopulation consisting of
partly isolated groups of organisms (demes) interconnected by migration. We
have shown that altruistic behavior coded by multiple substitutable genes can
stably coexist with selfish behavior, even under relatively high mutation and
migration rates, i.e. under such conditions where altruistic behavior coded by
a single gene is quickly outcompeted in a metapopulation.
