Altruism and kin selection
Sometimes an individual may behave in such a way that it is detrimental to itself, the donor, but beneficial to another individual, the recipient. This type of unselfish behaviour is called altruism.
Altruism may be common between individuals who are related (kin). The donor will benefit in terms of the increased chances of survival of shared genes in the recipient’s offspring or future offspring.
Reciprocal altruism occurs where the roles of the donor and recipient are later reversed. This often occurs in social animals.
For example, vampire bats feed only on blood. An individual cannot survive for longer than 70 hours without a meal. Bats that have fed will often regurgitate part of their blood meal into the mouth of a bat that has not fed.
Research has shown this is a reciprocal behaviour. Bats are more likely to provide a meal for a bat that has previously helped them in the same way.