“A population of organisms in the wild must have enough natural variation such that winners and losers can be picked. A flock of finches on an island, for instance, needs to possess enough intrinsic diversity in beak sizes such that a season of drought might be able to select birds with the toughest or longest beaks. Take that diversity away – force all finches to have the same beak – and selection comes up empty-handed. All the birds go extinct in a fell swoop. Evolution grinds to a halt. But.”
