The quality that organisms attempt (unconsciously) to maximize as the result of natural selection acting on genes that are influential in controlling their behaviour and physiology. It includes the individual’s own reproductive success (i.e. direct fitness, usually taken as the number of its offspring that survive to adulthood) and also the effects of the individual’s actions on the reproductive success of its relatives (i.e. indirect fitness), because relatives have a higher probability of sharing some identical genes with the individual than do other members of the population. When interactions between relatives are likely to occur (which happens during the lives of many animals and plants) kin selection will operate.