The Evolution of Alloparental Care and Adoption in Mammals and Birds

Alloparental care and adoption of young, aparently altruistic and reproductively costly behaviors, have been reported in over 120 mammalian and 150 avian species. Members of these taxonomically and ecologically diverse species often share similar behavioral and sociecological strategies in parental care, and may practice strikingly convergent forms of allopareting, such as "babysitting" behavior. Individuals that care for alien young may acquire selective advantages associated with increased inclusive fitness, parental experience, reciprocal altruis, and exploitation of fostered young. In many cases, environmental constraints, such as scare breeding resources of food sources requiring cooperative foraging strategies, appear to influence the occurrence of allopareting and adoption. In addition, proximate factors incorporating "reproductive errors" may be involved in some instances of fostering, Often, several selective benefits, along with various environmental pressures or reproductives mistakes may collectively promote the evolution of alloparental care and adoption. Fostering behaviors have been reported especially often in animals characterized by one or more of the following reproductive or social features, most of which are typical of K-selected species: (1) production of single offspring; (2) prolonged or energetically intensive parental investment; (3) limited lifetime reproductve output; (4) smal groups with tight kinship bonds; (5) highly social or cooperative group structure; and (6) young that are raised in high-density breeding colonies.