altruistic individual is better off materially. Between pairs, individuals in the pair with the highest degree of altruism are … better off materially. I determine the evolutionarily stable degree of altruism, allowing for assortative matching. The … stable degree of altruism is strictly smaller than the degree of assortativity, and it may be negative. It is also increasing …

equally altruistic siblings, their equilibrium effort is non-monotonic in the common degree of altruism, and it depends on the … harshness of the environment. We define a notion of local evolutionary stability of degrees of sibling altruism, and show that …