Final answer:
In the kin selection formula rb-c<0, the 'b' represents the 'benefit' relatives receive from an individual's altruistic behavior, contributing to their reproductive fitness. 'r' signifies the coefficient of genetic relatedness, and 'c' is the cost of the altruistic act to the individual.
Step-by-step explanation:
In the context of kin selection, which is a type of natural selection, the 'b' in the equation rb-c<0 represents the 'benefit' that relatives receive from an individual's altruistic behavior. This benefit is measured in terms of reproductive fitness, which can include a wide variety of things such as surviving to reproductive age, finding a mate, or actually having offspring. The 'r' in this equation refers to the coefficient of relatedness, which is a measure of how closely two individuals are genetically related. The 'c' stands for the cost to the individual performing the altruistic act.
Under kin selection, altruistic behavior is favored by natural selection if the cost incurred by the individual is less than the benefit multiplied by their genetic relatedness to the benefited individual—that is, rb>c. This concept helps to explain why individuals may perform acts that seem self-sacrificial on the surface; these acts can still increase the likelihood that their genes will be passed on through their relatives.