text: , marriage of a woman to two or more men at the same time; the term derives from the Greek polys, “many,” and anēr, andros, “man.” When the husbands in a polyandrous marriage are brothers or are said to be brothers, the institution is called Polygyny, the marriage of a man and two or more women at the same time, includes an analogous sororal form.
  Polyandrous cultures have devised several methods through which to designate the ancestry of the children of such marriages. In fraternal polyandry, the children are often said to be descended from the eldest brother alone, while in other cases fatherhood is established through a ceremony or the children are said to have descended from all the husbands equally.
  A related form of marital union, sometimes called annulment or divorce. Polyandry must be distinguished from privileged sexual access to a married woman, a practice that was fairly common in traditional cultures and was often associated with customs of kinship, hospitality, or fertility rites.
  Polyandry is, in fact, a rare phenomenon, if not as rare as once thought, and understanding of the variables that define the term is evolving. The two best-known areas in which polyandry was studied and continued to be practiced into the 21st century are the Plateau of Tibet (a region shared by India, Nepal, and the Tibet Autonomous Region of China) and the Marquesas Islands in the South Pacific. In a report published in 2012, however, anthropologists Kathrine Starkweather and Raymond Hames identified 53 additional nonclassical societies throughout the world (including North America and South America) that also practice polyandry, whether formal (i.e., recognized by marriage and co-residence) or informal (when two or more men are considered the co-fathers of offspring and are invested in the care of both mother and child or children). Polyandry is generally considered to be a response to peculiar localized conditions, among them sex (gender) ratios, adult male mortality, male absenteeism, social stratification, and the group’s economic basis. Virtually all societies in which the practice of polyandry is accepted are based on hunting and gathering or on agriculturalism.