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The evolution of modern human populations has been accompanied by dramatic changes in environment and lifestyle. In the last 100,000 years, behaviorally modern humans have spread from Africa to colonize most of the globe. In that time, humans have been forced to adapt to a wide range of new habitats and climates. Following the end of the last ice age, 14,000 years ago, there was a major warming event that raised global temperatures to roughly their current levels. Further dramatic changes occurred with the transition from hunter-gatherer to agricultural societies, starting about 10,000–12,000 years ago in the Fertile Crescent, and a little later elsewhere. This was also a period marked by rapid increases in human population densities. Increased population density promoted the spread of infectious diseases, as did the new proximity of farmers to animal pathogens [1,2].

Each of these kinds of changes likely resulted in powerful selective pressures for new genotypes that were better suited to the novel environments. Indeed, there are a number of recent reports of genes that show signals of very strong and recent selection in favor of new alleles: for example, in response to malaria [3–5]; at the lactase gene in response to dairy farming [6]; at a salt sensitivity variant in response to climate [7]; and in genes involved in brain development [8,9].

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[Copyright: © 2006 Voight et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.]

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