Genes and social habits
10 December 2009
Parts of the human genome are inherited only through one parent: mitochondrial DNA comes from the mother, while fathers always contribute a Y chromosome to their sons. Previous genetic studies in large populations suggest that, on average, mitochondrial DNA types are more geographically spread, and thus that women move around more.
The researchers developed a mathematical formula that relates differences in sex-specific and regular DNA to population size and migration. They sampled a number of populations in Central Asia, including Tajiks, Kazakhs, Karakalpaks, Kyrgyz and Turkmen.
Traditionally, most of these groups consist of herders organised into paternal descent groups that choose brides outside of their own social group. The Tajiks, in contrast, place equal importance upon male and female lines, and marry within their own social group, often to cousins.
The authors found the signature of the two different social organisations in the genomes of the current members of each society. As expected, the women seemed to move around more among the herders, as they live in their husbands’ villages, far from their birthplaces. But more surprisingly, the calculations suggest that there is a larger effective population of women compared with men in these populations - meaning that, within populations, men are more genetically related than expected, because of the importance of paternal descent in their social organisation.
Since humans aren’t the only ones with complex social dynamics, the methods in this study may also be useful for studying the ecology of animal species.
Image: Yurt family life, Dorgut, Mongolia; Mark de Fraeye/Wellcome Images
References
Ségurel L et al. Sex-specific genetic structure and social organization in Central Asia: insights from a multi-locus study. PLoS Genet 2008;4(9):e1000200.