Could recombination drive evolution?

The dominant model of evolution, known as the modern synthesis, holds that species variety arises mostly from point mutations, or changes in the individual nucleotides that make up DNA. Yet this model tends to ignore genetic recombination, a source of variation that occurs when an entire cluster of nucleotides is shuffled among chromosomes.

So Gene Levinson, a molecular biologist at the Genetics & IVF Institute in Fairfax, Va., devised a computer simulation of an evolutionary process that takes into account the effects of recombination.

"I represented DNA sequences in a genetic algorithm and subjected them to recombination or mutation to see how they evolved," Levinson says. "What I find is that recombination is more potent than mutation as a source of evolutionary change. With recombination, changes show up faster."

To look at the synergistic effects of natural selection and recombination, Levinson created three such algorithms. Each subjected representations of a DNA sequence to a specific type of recombination. For comparison, he allowed the same sequences to undergo point mutations. In addition, to simulate natural selection pressures, he varied the survival and attrition rates of the new DNA sequences.

With recombination, Levinson found, "the attrition rate, which is a weeding-out process, doesn't have to be nearly so extreme as it does with mutation to see evolutionary changes survive. Even a slight attrition rate with recombination can produce a dramatic effect, whereas with mutation, a small attrition rate produces only a small effect."

Natural selection, he believes, may even favor recombination. Recombination may also help explain how sexual reproduction has furthered evolution by diversifying species.

"A synergism between recombination and natural selection may have played a major role in Darwinian molecular evolution," Levinson says, "a role that is obscured by the semantics of the modern synthesis" theory