The evolutionary process usually acts to select the single best adaptation to help an organism survive, but sometimes it also works to maintain genetic variation in a population to keep the species’ hereditary options open. For example, humans can carry two versions of the hemoglobin gene: a normal one, and a mutated one that distorts the shape of red blood cells. People with two copies of the normal gene are at risk for contracting malaria, but those with one of each are partially protected from the disease, a potentially life saving benefit.
In a new genome-wide analysis study looking for evidence of long-lived examples of this genetic hedging, Molly Przeworski, a professor of human genetics and of ecology and evolution, uncovered at least six regions of the genome where humans and chimpanzees share the same variations. This suggests that the variations took place in a common ancestor of the two species, and may have had something do with the ability to fight off pathogens. From our Newsroom:
“When we looked for genetic clues pointing to other, more ancient, examples of balancing selection, we found strong evidence for at least six such regions and weaker evidence for another 119 — many more than we expected,” said study author Molly Przeworski, PhD, professor of human genetics and of ecology and evolution at the University of Chicago.
“We don’t yet know what their functions are,” she said. None of the six regions codes for a protein. There are clues that they are involved in host-pathogen interactions, “but which pathogens, what immune processes,” she said, “we don’t know.”
Leffler EM, Gao Z, Pfeifer S, Ségurel L, Auton A, Venn O, Bowden R, Bontrop R, Wall JD, Sella G, Donnelly P, McVean G, & Przeworski M (2013). Multiple Instances of Ancient Balancing Selection Shared Between Humans and Chimpanzees. Science (New York, N.Y.) PMID: 23413192