Abstract
The ways in which natural selection can allow the proliferation of cooperative behavior have long been seen as a central problem in evolutionary biology. Most of the literature has focused on interactions between pairs of individuals and on linear public goods games. This emphasis has led to the conclusion that even modest levels of migration would pose a serious problem to the spread of altruism through population viscosity in group structured populations. Here we challenge this conclusion, by analyzing evolution in a framework which allows for complex group interactions and random migration among groups. We conclude that contingent forms of strong altruism that benefits equally all group members, regardless of kinship and without greenbeard effects, can spread when rare under realistic group sizes and levels of migration, due to the assortment of genes resulting only from population viscosity. Our analysis combines group-centric and gene-centric perspectives, allows for arbitrary strength of selection, and leads to extensions of Hamilton’s rule for the spread of altruistic alleles, applicable under broad conditions.
Highlights
The evolution of cooperation and altruism are fundamental scientific challenges highlighted by their role in the major transitions in life’s history, when natural selection acted simultaneously on several competing levels [1,2,3,4,5,6,7,8]
We show that for iterated public goods games, in which altruists cooperate or not in each round based on previous outcomes [35,36], altruism can spread even when cost/benefit ratios for each altruistic act are reasonably high, groups are large, selection is weak and migration rates are substantially larger than the inverse of group size
A Basic Example: Iterated Public Goods Game Non-linearities in life-cycle payoffs can result from activities repeating themselves during a lifetime, and behavior being contingent on previous outcomes
Summary
The evolution of cooperation and altruism are fundamental scientific challenges highlighted by their role in the major transitions in life’s history, when natural selection acted simultaneously on several competing levels [1,2,3,4,5,6,7,8] In this context, the relevance of basic concepts, including group selection and Hamilton’s rule remain controversial [9,10,11,12,13,14,15,16,17,18]. This is obtained in a mathematically rigorous way, by analyzing the stability of the equilibrium in which this allele is absent This analysis is done for arbitrary strength of selection, but when selection is weak and groups are large the condition for invasion simplifies significantly into a form that is easy to apply and provides substantial intuition. Our results show that one of the most widely used approaches to analyzing kin selection models, [19], [7](condition (6.7)), and [16](Box 6), yields incorrect results in some biologically relevant situations
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