Parasites drove human genetic variation

MODERN humans began to spread from Africa approximately 100,000 years ago. They settled in distant lands, where they had to adapt to unfamiliar climates, find different ways to feed themselves, and fight off new pathogens.A study now suggests that it was the pathogens, particularly parasitic worms, that had the biggest role in driving natural selection ' but that genetic adaptation to them may also have made humans more susceptible to autoimmune diseases.Populations separated by distance tend to drift apart genetically over time, and roughly 95 per cent of variability between populations is a result of that drift. But the local environment plays a part too. Genetic variants that improve survival in a given region tend to become more common in the population that lives there. By looking for correlations between the frequency of different variants in a population and environmental factors such as climate, researchers can gain a better understanding of the drivers of human adaptation.The authors of a study published last week in PLoS Genetics1 used data from more than 1,500 people, representing 55 distinct populations, to calculate the frequency of different genetic variants. They then developed a statistical model to predict the distribution of these variants. The model incorporates three types of environmental variable that could have exerted selective pressure on the human genome: climate; the importance of subsistence strategies such as agriculture, fishing and animal husbandry; and pathogen diversity.'Our goal was to understand which category most shaped human genetic variation,' says Matteo Fumagalli, a genomics researcher at the University of California, Berkeley, and lead author of the paper.The researchers removed the variables from the model one at a time, to see which would have the biggest impact on the predictive power of the model.
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