standing variation

Eyre-Walker A 2006 Size does not matter for mitochondrial DNA. Science 312:537-538.

• if Bazin et al. are correct and the diversity of mitochondrial DNA, and perhaps nuclear DNA, is limited by repeated adaptive substitution, then the rate of adaptation is dependent on the rate of mutation, not the rate at which the environment changes
• it simply means that no species is ever perfectly adapted and that adaptive mutations can always occur in any species
• this further implies that most adaptive mutations arise de novo and do not come from genetic variation that is already segregating in the population

• it is ironic that the lack of recombination, once seen as a great asset of mitochondrial DNA, may be something of a problem in this context