Leaping Mutants

Statistical analysis of the proximity of point mutations has suggested a mechanism by which eukaryotic cells could acquire a group of mutations all at once. “A similar phenomenon had been observed in bacteria,” says Dr. Matthew Hahn. “And the idea that this might be happening in eukaryotes has been around for a while. We are the first ones to use exhaustive genomic studies to show it’s actually happening, and happening in a big way.”

“An organism could improve its fitness if it acquired multiple mutations that would each reduce fitness if they occurred individually,” adds graduate student Schrider. "The less-fit intermediate states would be eliminated by natural selection. Cases like this are referred to as ‘fitness valleys.’”

Thus, a group of mutations might produce a desirable change in an organism, but any one of those mutations individually could be harmful. Dr. Hahn is proposing a mechanism by which all the needed mutations could be acquired at once, avoiding the unfit intermediate state. His group analyzed the genomes of yeast, roundworms, a plant, and humans. They found that about three percent of mutations were near other mutations. Dr. Hahn believes such “multi-nucleotide mutations (MNMs)” have “a near-100 percent likelihood of being caused by the same mutational event.”

However, he does not know of any actual examples of “valley leaping.” While a defective DNA polymerase molecule might make a series of errors, he does not know whether the MNMs he has found conform to that mechanism.

Bacteria do not acquire information to become anything other than bacteria.

The bacterial analogy to which he refers is the horizontal transfer of genomic islands, which seems to be a way God designed for bacteria to exchange information. However, bacteria do not acquire information to become anything other than bacteria.

Likewise, even if eukaryotic cells from yeast, roundworms, plants, and humans happen to acquire a bundle of genes that leap over a fitness valley, those cells will still be yeast, roundworm, plant, and human cells. The change will be horizontal, not vertically up the evolutionary ladder.