Or to put it in less complex terms, the natural variation seen in a species. This is a slightly timely post following on from that of yesterday on natural selection. Here is a concise demonstration of the variation seen which nature can then act on. In this case it’s the coat colour of fallow deer. These individuals live in a London park and as such are not exactly open to the full rigours of natural selection, but the variation is certainly natural and that’s what we are interested in.
Fallow deer normally look like the individual on the far left – a light-medium brown with a lighter underside and white dapples down the body. However, you can also see a near spot-less animal on the far right (fewer spots and much more faint than usual), a much darker and spotless animal and behind that and to the right, a near black one. Over on the left at the rear (though not very clear) is a nearly all-white stag. Thus while obviously part of a continuum, we can see white, light, normal, dark and near black forms in this small herd. Natural variation has generated quite a choice and it’s easy to extrapolate a little and see that heavy snow over a number of years might select for a better camoflaged white gene to dominate or a new nocturnal predator to have trouble spotting black individuals at night. The variation is there, it just needs some selection to drive it one way or the other and a profound change might rapidly be evident in the population.