Barcelona, Spain. Changes in social structure and cultural practices can also contribute to human evolution, a study finds.

Researchers hypothesize that co-evolution based on the pairing of genetics and culture could in fact be the dominant model throughout the history of the human evolution.


Scientists compared patterns of genetic, geographic, climatic, and physical characteristics for 1,203 individuals from six South Amerindian populations living in the Brazilian Amazon and Central Plateau, including the Xavánte, Kayapó, Baniwa, Ticuna, Kaingang, Yanomama and Otomí groups. The last three populations form a single group of recently diverged speakers of the Jê language.

Research Participants

Tábita Hünemeier is the lead author, with contributions from the lecturer Mireia Esparza and assistant Neus Martínez-Abadías, from the Anthropology Unit of the Department of Animal Biology at the Universidad de Barcelona (UB).

Rolando González-José from the Patagonian National Research Center (CENPAT-CONICET) in Argentina provided overall coordination of the study.

Their current findings appear in the Proceedings of the National Academy of Sciences (PNAS).According to the authors, one of the most interesting results is the rapid rate of morphological change in the Xavánte, which is up to 3.8 times faster than in the other groups. Detailed analyses of head measurements determined that the Xavánte are the most differentiated population, having larger heads, taller and narrower faces, and broader noses compared with the other groups. These traits evolved about 3.8 times faster than the evolutionary rates of the other groups.

The changes observed in the Xavánte follow an integration pattern of human skull shape recently described in the literature. "This study demonstrates that when selection acts in the same direction as integration patterns, evolution is favoured," explain Mireia Esparza and Neus Martínez-Abadías.

The divergence was independent of climate differences or the Xavánte's geographical separation from the other five populations but could reflect a combination of culturally mediated isolation plus sexual selection.

A prior study found that a fourth of the population of one Xavánte village were sons of a single chief who had five wives, the researchers note, suggesting that sexual selection may favor wealthy and well-positioned men and could therefore affect evolution in Xavánte society. Esparza and Martínez-Abadías also co-authored a parallel study on morphometric patterns and the evolutionary potential of the human skull.

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