Geneticist Sarah Tishkoff splits her time between her laboratory at the University of Pennsylvania in Philadelphia and remote parts of Africa.
She works with and collects DNA from people as diverse as hunter-gatherers in the jungles of central Africa; grain-growing farmers in southern Africa; and nomadic, cattle-raising warriors in eastern Africa.
By designing computer models to compare the DNA of these different populations, she hopes to track down gene variations that make some people less susceptible to malaria—one of the world's leading causes of death.
People in certain African tribes that have been exposed to malaria for thousands of years can contract the disease and survive it. These tribespeople developed genetic adaptations that gave them natural resistance to malaria, which they passed on to their descendants. Through the generations, the resistance genes have become more common in the population.
Tishkoff calls this process the "footprints of natural selection." Following the trail can lead scientists to the genetic basis of innate resistance—and possibly to future therapies—for malaria and other diseases.
So far, the trail has taken Tishkoff to data indicating that innate resistance to malaria is caused by a variant in the gene for a specific enzyme nicknamed G6PD. People with this genetic variant make less of the enzyme, which is needed for several important chemical reactions inside cells.
Up to one-quarter of the people living in malaria-infested regions of Africa have this variant. Everywhere else, fewer than 5 percent have it.
Understanding how the G6PD genetic variant protects people from malaria could eventually help treat and prevent the spread of the disease. The work, Tishkoff adds, is also helping to unravel the history of modern humans in Africa and beyond.