In biology, altruism refers to behaviour by an individual that increases the fitness of another individual while decreasing their own. Altruism in this sense is different from the philosophical concept of altruism, in which an action would only be called "altruistic" if it was done with the conscious intention of helping another. In the behavioural sense, there is no such requirement. As such, it is not evaluated in moral terms—it is the consequences of an action for reproductive fitness that determine whether the action is considered altruistic, not the intentions, if any, with which the action is performed.
Cooperative hunting by wolves allows them to tackle much larger and more nutritious prey than any individual wolf could handle. However, such cooperation could, potentially, be exploited by selfish individuals who do not expose themselves to the dangers of the hunt, but nevertheless share in the spoils.
Olive baboons grooming
A male peacock with its beautiful but clumsy, aerodynamically unsound tail—a handicap, comparable to a race horse's handicap.
The best horses in a handicap race carry the largest weights, so the size of the handicap is a measure of the animal's quality
Kin selection is a process whereby natural selection favours a trait due to its positive effects on the reproductive success of an organism's relatives, even when at a cost to the organism's own survival and reproduction. Kin selection can lead to the evolution of altruistic behaviour. It is related to inclusive fitness, which combines the number of offspring produced with the number an individual can ensure the production of by supporting others. A broader definition of kin selection includes selection acting on interactions between individuals who share a gene of interest even if the gene is not shared due to common ancestry.
The co-operative behaviour of social insects like the honey bee can be explained by kin selection.
Charles Darwin wrote that selection could be applied to the family as well as to the individual.
The evolutionary biologist John Maynard Smith used the term "kin selection" in 1964.
Kin recognition: theory predicts that if the bearers of a trait (like the fictitious 'green beard') will behave altruistically towards others carrying a green beard, altruistic traits that are genetically linked to the green beard gene will have a selective advantage.