New research on the genomes of African Americans has revealed evidence of natural selection that began with ancestors' adaptations to the harsh conditions in America.
The findings are reported in the journal Genome Research  and include the conclusion that certain disease-causing variant genes became more common in African Americans, possibly because they conferred greater, offsetting benefits.
The researchers say some of the gene variants, like the one for sickle-cell hemoglobin (which, in single-dose form, protects against malaria) have become less common over time. They believe this is because, in America, malaria is much less of a threat than in Africa.
Why are the scientists studying the African-American genome? Because most searches for variant genes that cause disease are done on people of European ancestry, and physicians want to ensure they haven't missed variants that may be more common in African Americans and helpful for developing treatments or diagnosis.
"Most of the genes associated with African-American ethnic diseases," the scientists behind the study explain, "may have played an important role in African Americans' adaptation to local environment."
Read more at the New York Times.