Adoption and foster parenting: an evolutionary enigma?

Adoption and foster care posits itself as an evolutionary paradox, especially when there is no kinship involved. Adopting non-related eggs or infants proximately comes with a cost in the form of sharing resources and can lead to death of own progeny in extreme cases. However, in most of the cases, the foster parents derive some fitness benefits from a foster child, which seems to be the ultimate causation and hence has evolved in different species across various taxonomic classes. Adoptions are also reported among members of two different species which is an interesting scenario and calls for further research and experimentation in order to determine if any evolutionary fitness benefits accrue due to such behaviour. Similarly, "brood parasitism" a form of "forced foster care" is a live example of biological species at arms race. In this short review, we provide cost and benefit analysis of adoption among genetically related and unrelated individuals with a special emphasis on brood parasites.