In social anthropology, polyandry refers to a marital practice in which a woman has more than one husband simultaneously.
In rural regions of India, Nepal, China (in particular, Yunnan province), and surrounding nations, fraternal polyandry, in which two (or more) brothers marry the same woman, is culturally accepted. Polyandry is also the accepted norm in a few African societies.
The term has been taken over into sociobiology, where polyandry refers, analogously, to a mating system in which one female forms more or less permanent bonds to more than one male. It can take two different forms. In one, typified by the Northern Jacana and some other ground-living birds, the female takes on much the same role as the male in a polygynous species, holding a large territory within which several males build nests, laying eggs in all the nests, and playing little part in parental care. In the other form, typified by the Galapagos Hawk, a group of two or more males and one female collectively care for a single nest. The latter situation more closely resembles typical human polyandry. These two forms reflect different resource situations: polyandry shared parental care is more likely in very difficult environments, where the efforts of more than two parents are needed to give a reasonable chance of rearing young successfully.