You'll often hear those in the anti-evolution crowd express the viewpoint that evolution by natural selection can't operate to increase genetic diversity, only to decrease it. That's a clue to their fundamental misunderstanding of how the process works. It's driven by mutations, changes in the genome. Those changes create the variation on which selection can operate. No changes, no variation, no evolution.

So, it goes without saying that the faster the rate at which mutations accumulate, the greater the amount of variation in the genome. True, a lot of that variation will be selectively neutral, or even detrimental. But if we assume a more or less constant chance of a favorable mutation, then the rate at which evolution proceeds must be tied in some fashion to the mutation rate.

So, what is that mutation rate? A study just published in the new issue of the journal Science examines mutation rates in Arabidopsis, a small flowering plant in the mustard family which has become a significant model organism for geneticists and for which the entire genome has been sequenced. The researchers followed five lines of Arabidopsis thaliana for 30 generations, and identified in each line the the changes occurring between the original ancestor and the final generation.

They found, in each line, some 20 base pair changes. Taking into consideration the 120 million base pair size of the Arabidopsis genome, this indicates that the probability that any given base changes in a given generation is about one in 140 million, or that each seedling likely contains one mutated base in each of the two copies of the genome in its diploid state.

To some, this may seem like a vanishly small number, and suggest that evolution must proceed slowly. However, when you consider a large population of Arabidopsis, each producing vast numbers of seeds in each generation, it becomes clear that the raw material is there to allow selection to go to work to produce relatively rapid changes.