I believe it was Bryan Caplan who introduced me to the analogy of a child’s personality being like a rubber band; parents, in particular adoptive parents, can twist and pull a child in particular directions so long as the child is under their direction, but once the child leaves the home the rubber band “snaps back.” This is basically communicating the fact that heritabilities on many psychological traits increase as people age. Concretely, adopted children resemble their biological parents more and more in their outcomes and dispositions as they mature. This can probably be explained in part by gene-environment correlations and positive feedback loops. I wouldn’t be surprised if this is most evident in WEIRD populations which are the targets of behavior genetics studies, because of the importance of individual choice and self-actualization once one reaches adulthood in WEIRD societies. If you are Amish or a Fundamentalist Mormon it may be that there isn’t enough environmental variation for gene-environment correlation to ever become particularly powerful.
This is a good example for my overall view of human nature. Rather than there being absolute universals (never say never), at least among the kind of thing people find interesting to argue about (nobody is interested in the fact that air-breathing is a human universal), there are tendencies. Polyandry goes strongly against human tendencies, but under some conditions can exist as a cultural norm. But, as people get more money, they rebel against the culture of polyandry.
This was my basic thought as well. But one thing I would add in the context of India: the rise of mass media and a common national elite culture has resulted in a great deal of homogenization in regards to particular values over the past 150 years. For example, many Indian groups have shifted from brideprice to dowry systems over the past 100 years as part of a process of “Sanskritization.” In Kerala high status Nairs abandoned the Sambadam practice in part due to to the fact that it seemed deviant and immoral to other Indian elite groups. It is also relatively well know that many Indian Muslims who were not of the Turco-Persian (at least in part) elite tended to have relatively syncretistic practices until recently, but Islamic “reform” movements have progressively aligned Indian non-elite Muslims with elite practices and identity (the founder of Pakistan was arguably from a syncetristic background, a possibility which is obviously not emphasized in modern Paksitan). But something similar has also occurred with groups which identify as Hindu, even if it is not as explicit because of Hinduism’s more decentralized nature. In other words the natural predispositions of humans, in particular males, to avoid polyandrous relationships when possible has probably been amplified by cultural norms which have spread and encouraged conformity to the preferred ideal.