Humans Only Mildly Polygamous

New genetic information shows that human societies have tended towards monogamy.

It has long been assumed that, but for the constraints of human society, men would mate with as many women as they could. Tiger Woods is but the most recent example, but the fact remains that human society has through its history been far more successful at maintaining reproductive equality between the sexes than would be expected from the male tendency to stray.

A paper by Canadian scientists in the American Journal of Human Genetics has confirmed this, but in doing so, it has also suggested that not all human societies are equal in this matter.

To understand the measure they have used, consider a society where each man partners two women and has a child by each. In such a society, the ratio of female genetic contribution to the male genetic contribution is 2:1. In general, this ratio approximates the technical measure termed Beta by the scientists in their paper. In monogamous societies, Beta should be one, while in polygamous societies it should be greater than one. Their results arrive at a Beta measure of 1.4 for the Yoruba tribe of West Africa, 1.3 for West Europeans and 1.1 for East Asians, which suggests that the male and female contribution to the population in East Asian society is far more equal than it is in the Western European population.

The work they have done, though, is not about current trends, but a compendium of the genetic history of the populations concerned. They have arrived at this measure by comparing the X chromosome with the non-sex chromosomes or autosomes. Since males have only one X chromosome, during recombination after fertilisation the X chromosome can only exchange genetic data with the chromosome that has come from the female, thus providing a record of the maternal contribution. The scientists have been able to extract this information and use it to provide a robust measure that works not across populations but across species.

The research, though, now raises the question of why such differences exist between human populations.

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Hartosh Singh Bal