The findings were published online this week for the journal Public Library of Science Biology in a paper titled "Population History and Natural Selection Shape Patterns of Genetic Variation in 132 Genes." For the paper, researchers studied the molecular evolution of 132 genes by comprehensively resequencing them in 24 African-Americans and 23 European-Americans. The results showed strong evidence for natural selection at eight genes in the European-American population, likely explained by the different environmental conditions people encountered as they moved into Europe sometime between 25,000 to 50,000 years ago.
"Our results suggest that the migration of humans out of Africa into new environments was accompanied by genetic adaptations to emergent selective forces," said Dr. Joshua Akey, lead author of the paper and an assistant professor in the Department of Genome Sciences at the University of Washington in Seattle.
If you were to compare the genomes of two randomly selected individuals you would find that they are not identical, but on average contain differences every 1,000 base pairs or so. The most common form of these differences is "single nucleotide polymorphisms," or SNPs (pronounced 'snips').
Occasionally, new SNPs arise that allow certain individuals in a population to be healthier and produce more offspring, and these variants become more frequent through the process of natural selection. Although there is considerable interest in finding regions of the human genome that have been targets of natural selection, the tools and resources needed to do so are only now becoming widely available.