Rate of evolution

The rate of evolution is a variable of considerable interest in evolutionary biology. It concerns the limits of adaptation to natural environments as well as the limits of artificial selection.

Humans have created a wide range of new species, and varieties within those species, of both domesticated animals and plants. Other human activity also impacts evolution. This has been achieved in a very short geological period of time, spanning only a few tens of thousands of years, and sometimes less. Maize, Zea mays, for instance, is estimated to have been created in what is now known as Mexico in only a few thousand years, starting between about 7 000 and 12 000 years ago, from still uncertain origins. In the light of this extraordinarily rapid rate of evolution, through (prehistoric) artificial selection, George C. Williams and others, have remarked that:

The question of evolutionary change in relation to available geological time is indeed a serious theoretical challenge, but the reasons are exactly the opposite of that inspired by most people’s intuition. Organisms in general have not done nearly as much evolving as we should reasonably expect. Long term rates of change, even in lineages of unusual rapid evolution, are almost always far slower than they theoretically could be. The basis for such expectation is to be found most clearly in observed rates of evolution under artificial selection, along with the often high rates of change in environmental conditions that must imply rapid change in intensity and direction of selection in nature.

Evolution is imposed on populations. It is not planned or striven for in some Lamarckist way. The mutations on which the process depends are random events, and, except for the "silent mutations" which do not affect the functionality or appearance of the carrier, are thus usually disadvantageous, and their chance of proving to be useful in the future is vanishingly small. Therefore, while a species or group might benefit from being able to adapt to a new environment by accumulating a wide range of genetic variation, this is to the detriment of the individuals who have to carry these mutations until a small, unpredictable minority of them ultimately contributes to such an adaptation. Thus, the capability to evolve is close to the discredited concept of group selection, since it would be selectively disadvantageous to the individual.

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