If that is the case, then why are both tasters and nontasters still present in the human population? Based on the rules of natural selection, shouldn’t all of the nontasters have died off early in our evolution? The answer is complex, Dr. Wooding said, noting that some things that taste bitter are used as medicine, such as compounds in certain tree barks that help protect against malaria. He and his colleagues—Drs. Dennis Drayna and Un-kyung Kim at the National Institutes of Health, along with Drs. Lynn Jorde and Michael Barnshad at the University of Utah—analyzed the gene for PTC sensitivity for certain “signatures” of natural selection that would tell them how the gene has changed over time. They found very strong evidence that within humans, a process called “balancing natural selection” has taken place. “This is a kind of natural selection that keeps two different forms of the same gene active in a population,” Dr. Wooding said. “In this case they are the taster and the nontaster forms. In the absence of this type of natural selection, you would expect one form to dominate. That hasn’t happened here because for some reason, there is not a strong advantage of one over the other. It’s an unusual situation.”
——————————-
70-569 | 70-571 | 70-577 | 70-579
