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Did Parasites Drive Human Evolution?

By Veronique Greenwood
Nov 16, 2011 11:37 PMNov 20, 2019 4:52 AM


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Hookworms are longer-lived than viruses and bacteria; they could have had a more significant effect on human evolution.

Humans live in all sorts of places---high deserts, tropical lowlands, frigid tundra. Over the millennia, you'd expect each population's assortment of genes to evolve to reflect the demands and dangers of its home environment: those who live in the deserts would possess genes for extra skin pigments to help keep their tender integument from burning (like African peoples), and those who live in sub-zero climes much of the year would have genes that keep them well-insulated in fat (like the Inuit). But what if factors other than climate, like the food available nearby or the viruses, bacteria, and parasites native to the area, also had an effect on various human populations' genetic toolkits? It's a fascinating question, but, given that we have to reconstruct all this supposed evolution from the current state of modern genomes, finding an answer isn't easy. A recent paper

takes an important first step by looking for correlations between 500,000 different genetic markers and certain environmental characteristics, like humidity, temperature, the local diet, and the prevalence of parasites and other pathogens. The researchers started out with the genetic information (specifically, their single nucleotide polymorphisms

, or SNPs, small differences in the genetic code) of 1,500 people hailing from 55 different populations, including two groups of Bantus

, Uygur

, and French Basque

, and a list of environmental measurements (you can check out their starting data in the three Excel tables here

). Most of the genetic variation between populations turned out be to attributable to drift (the gradual differences that build up between populations that don't interbreed much), but they did find that some noticeable differences were related to pathogens, food, and climate, with pathogens, parasites especially, having the lion's share. This suggests that parasites could have driven human evolution, the researchers write, and they opine that this might be because parasites like helminth worms have relatively long life-cycles, so humans had a chance to evolve adaptations to combat them, while short-lived bacteria and viruses might not be causing such strong effects. There are still plenty of gray areas in this realm of population genetics

, as outside experts interviewed by Nature News point out

: it's likely that climate, food, and pathogens are closely intertwined as sources of human evolutionary pressure (and furthermore, this study found correlations---not causation). But this paper is an interesting step forward in exploring what forced us to evolve.

Image courtesy of CDC / Wikimedia Commons

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