 This simple model also highlights the point made previously, that donor-recipient correlation, rather than genetic relatedness, is the key to the evolution of altruism. What is needed for altruism to evolve, in the model above, is for the probability of having a partner of the same type as oneself to be sufficiently larger than the probability of having a partner of opposite type; this ensures that the recipients of altruism have a greater than random chance of being fellow altruists, i.e., donor-recipient correlation. Whether this correlation arises because partners tend to be relatives, or because altruists are able to seek out other altruists and choose them as partners, or for some other reason, makes no difference to the evolutionary dynamics, at least in this simple example. 