In one of the first studies to scientifically prove an evolutionary advantage for sex, a researcher at Wake Forest University reports in the July 31 issue of the journal Nature that sex helps weed out harmful genetic mutations, increasing a population's genetic fitness.
Clifford Zeyl, assistant professor of biology at Wake Forest University, said that his studies of sexual reproduction in brewer's yeast, Saccharomyces cerevisiae, have found that sexual populations are better at removing undesirable genetic mutations than single-sexed yeast.
"Why sex evolved is one of the big unanswered questions of evolutionary biology," Zeyl says. "This is one of the first examples of finding an evolutionary advantage for sex.
"Vertebrates are almost all sexual, and the persistence of sexual reproduction is one of the great mysteries of evolution. This might be an explanation for why we turned out to be sexual and why we evolved to have two parents instead of just cloning ourselves."
Genetically speaking, sexuality is more than a little messy, Zeyl admits. Why go to the trouble of disrupting such precisely constructed genetic complexes if you can only transmit half of your genes to your children? After all, asexual organisms can pass on all of their genes to subsequent generations of clones.
One other explanation for the evolutionary benefit of sex was that it produces novel and interesting genetic combinations required for adapting to environmental changes. But Zeyl and colleague Graham Bell of McGill University in Montreal found that wasn't the case with yeast. Sexually active yeast fared no better in new environments than asexual yeast.
"In most respects, cloning is a much more efficient way of
reproduction," Zeyl says, "but if you have a whole population of organisms who
are sexual, it appears more likely that they will carry around fewer mutations.
Contact: Wayne Thompson
Wake Forest University