Historically, polyandry was much more common than we thought.
For generations, anthropologists have told their students a fairly simple story about polyandry -- the socially recognized mating of one woman to two or more males. The story has gone like this:
While we can find a cluster of roughly two dozen societies on the Tibetan plateau in which polyandry exists as a recognized form of mating, those societies count as anomalous within humankind. And because polyandry doesn't exist in most of the world, if you could jump into a time machine and head back thousands of years, you probably wouldn't find polyandry in our evolutionary history.
That's not the case, though, according to a recent paper in Human Nature co-authored by two anthropologists, Katherine Starkweather, a PhD candidate at the University of Missouri, and Raymond Hames, professor of anthropology at the University of Nebraska. While earning her masters under Hames' supervision, Starkweather undertook a careful survey of the literature, and found anthropological accounts of 53 societies outside of the "classic polyandrous" Tibetan region that recognize and allow polyandrous unions. (Disclosure: I first learned of Starkweather's project while researching a controversy involving Hames and he is now a friend.)
Indeed, according to Starkweather and Hames, anthropologists have documented social systems for polyandrous unions "among foragers in a wide variety of environments ranging from the Arctic to the tropics, and to the desert." Recognizing that at least half these groups are hunter-gatherer societies, the authors conclude that, if those groups are similar to our ancestors -- as we may reasonably suspect -- then "it is probable that polyandry has a deep human history."
Rather than treating polyandry as a mystery to be explained away, Starkweather and Hames suggest polyandry constitutes a variation on the common, evolutionarily-adaptive phenomenon of pair-bonding -- a variation that sometimes emerges in response to environmental conditions.
What kind of environmental conditions? Well, "classical polyandry" in Asia has allowed families in areas of scarce farmable land to hold agricultural estates together. The marriage of all brothers in a family to the same wife allows plots of family-owned land to remain intact and undivided."
In other cultures, it appears that a man may arrange a second husband (again, frequently his brother) for his wife because he knows that, when he must be absent, the second husband will protect his wife -- and thus his interests. And if she gets impregnated while Husband #1 is gone, it will be by someone of whom he has approved in advance. Anthropologists have recorded this kind of situation among certain cultures among the Inuit (the people formerly called Eskimos).
Then there's the "father effect" demonstrated by Penn State's Stephen Beckerman and his colleagues in their study of the Bari people of Venezuela. The Bari have a system for recognizing two living men as both being fathers of a single child. Becerkman's group found that children understood to have two fathers are significantly more likely to survive to age 15 than children with only one -- hence the term "father effect."
Two fathers? As odd as it can sound to those of us who know of human development as the one-egg-meets-one-sperm story, some cultures maintain the idea that fetuses develop in the womb as the result of multiple contributions of semen over the course of a pregnancy. In cultural systems of what Beckerman has named "partible paternity," two men can be socially recognized as legitimate fathers of a single child. Starkweather and Hames call this a form of "informal polyandry," because while the two fathers may not be both formally married to and living with the mother in all cases, the society around them officially recognizes both men as legitimate mates to the mother, and father to her child.
What all these polyandrous situations -- classical and non-classical, formal and informal -- have in common is that they are all socially recognized systems in which women may openly have multiple mates simultaneously. Women in such systems are not "cheating" by any stretch of the imagination, nor are the men being cuckolded. The systems are socially sanctioned. But this does not mean that the women are in control of the arrangements; in many of the cultures Starkweather and Hames reviewed, the first husband functions as the decider when it comes to resource distribution and acceptance of additional male mates.
So how is it that, in spite of all this evidence of polyandry accumulating steadily in the literature, anthropologists for so long passed along the "it's virtually non-existent" story? Starkweather and Hames suggest anthropology has been accidentally playing a scholarly version of the Telephone Game.
In 1957, George Murdock defined polyandry in a seminal text as "unions of one woman with two or more husbands where these [types of union] are culturally favored and involve residential as well as sexual cohabitation." Using such a strict definition, Murdock could accurately say polyandry was extremely rare; almost no cultures have polyandry as the dominant and most preferred form of family life.
Then subsequent scholars mis-repeated Murdock's remark; polyandry went from being understood as "rarely culturally favored" to "rarely permitted." Thus mating diversity that was known to exist became relatively invisible in the big story told by anthropology about human mating. (If you write off every exception to a supposed rule, you will never think to challenge the rule.)
In an email interview with me, Starkweather remarked, "I don't think that anyone, including Murdock, was operating from an explicitly sexist standpoint. However, I do think that the definitions of polyandry, and thus perceptions about its rarity, may have been due at least in part to the fact that an overwhelming percentage of anthropologists collecting data and shaping theory at the time were men." During Murdock's time, "there seemed to be a fairly pervasive belief that polyandry didn't make any sense from a male's perspective."
That explanation -- that Western male anthropologists had a hard time "believing" in polyandry -- makes sense. Humans appear prone, on average, to sexual jealousy, and so it would not be unreasonable for many of us -- men and women alike -- to project an assumption that sexual jealousy would make poly-unions untenable. Indeed, anthropologists have found that in both polyandry (one woman, multiple husbands) and polygyny (one husband, multiple wives), sexual jealousy often functions as a stressor in families around the world.
Yet certain environmental circumstances do seem to increase the odds of a culture accepting some form of polyandry. In particular, Starkweather and Hames find that polyandry is often found in societies with highly skewed "operational sex ratios." Translation: When fertile women are scarce, men are more likely to be found openly sharing women. Indeed, fully three-quarters of the 53 societies identified by Starkweather and Hames involve skewed sex ratios, with more adult males than females.
This led me to wonder, in our exchange, whether in places where sex ratios are becoming highly skewed -- in places like India and China -- is polyandry likely to emerge? Starkweather and Hames guess not. First, most of the cultures in which polyandry is found look very different from modern India and China; polyandry shows up mostly in relatively egalitarian societies (i.e., societies with very simple social structures, without massive governmental bureaucracies and elaborate class structures). So, for example, polyandry is regularly found among the South American Yanomamö, the people Hames studied in the field in the 1970s and 1980s.
Modern India and China don't look anything like simple egalitarian societies. So what will happen there? Hames points out that, "Landowning societies all over the world have faced an excess of men at one point or another and have dealt with this by sending these men to the priesthood, to fight in wars, or to explore or make a name for themselves" elsewhere. He concludes, "It is clear that these countries will have to do something with all of the excess men, but polyandry will probably not occur as a widespread solution."