Cooperative Breeding - Evolution

Evolution

Generally the helpers in cooperatively breeding birds and mammals are relatives of the dominant breeders who still remain in the group or are individuals whose own breeding attempts have been unsuccessful and have come back to their original group to help with kin.

Kin selection was previously thought to be one of the major contributing factors to the evolution of cooperative breeding. Kin selection is when individuals increase their fitness through indirect benefits by helping relatives. Today, kin selection is not a compelling explanation for the evolution of cooperative animal societies for a number of reasons. Most permanent groups of social animals are composed of relatives, and it is unclear if the degree of relatedness is consistently higher in cooperative breeders than in other species that simply live in stable groups that don’t breed cooperatively. There are many studies of cooperative birds and mammals that have shown that unrelated helpers can invest just as much as close relatives. Another reason why kin selection doesn’t fully explain the evolution of cooperative breeding is that the relative importance of indirect fitness benefits of helpers has probably been overestimated. Many times, the benefits received by the helpers and those they confer on kin have both been included, leading to a double accounting of kin-selected benefits.

Today, there is growing support for the theory that cooperative breeding evolved by means of some form of mutualism or reciprocity. Mutualism is a form of symbiosis that is beneficial to both involved organisms. Mutualism has many forms and can occur when the benefits are immediate or deferred, when individuals exchange beneficial behaviors in turn, or when a group of individuals contribute to a common good, where it may be advantageous for all group members to help raise young. When a group raises young together, it may be advantageous because it maintains or increases the size of the group. The greatest amount of research has been invested in reciprocal exchanges of beneficial behavior through the iterated prisoner's dilemma. In this model, two partners can either cooperate and exchange beneficial behavior or they can defect and refuse to help the other individual.

Research has found that there is not one theory that can explain the evolution of all cooperative breeding species. In addition to mutualism and reciprocity, group augmentation has been suggested as one way cooperative breeding could have evolved in some species. Group augmentation occurs when animals living in a group behave in a way that increases the group's size. This type of behavior would be selected for if larger groups increased the individual's chances of survival. This ultimately would select for individuals that help raise other animals' offspring.