C < Rb

Synonyms

Altruism between relatives; Hamilton’s Rule; Kin-altruistic behaviour.

Definition

The cost of an altruistic act to the donor must be less than the benefit, weighted by relatedness, to the recipient.

Introduction

How is an altruistic act favored by natural selection if it incurs a cost to the actor? As the behavior would have a detrimental impact on the actor’s reproductive success, the genes that facilitate the expression of that behavior would be less likely to be passed on and should decrease in the gene pool. Hamilton (1964) recognized the importance of the relatedness coefficient in the evolution of altruism, incorporating it in a formula to explain kin-selected (Maynard Smith 1964) altruistic behavior.

Imagine a scenario where an individual sacrifices its own life to save others. One copy of the kin-altruistic gene is lost from the gene pool when the actor dies, but if ten close relatives are saved as a result of the sacrifice, several copies of the kin-altruist gene are...