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There are good reasons why natural selection has become widely accepted as an explanation of evolutionary development. When applied to mammals and other large animals, it fits perfectly. But we cannot assume that all evolutionary steps arise from selection, particularly when looking at smaller animals.

At a minimum, in explaining evolutionary pathways through time, the constraints imposed by history rise to equal prominence with the immediate advantages of adaptation.

It was a shock to people of the nineteenth century when they discovered, from observations science had made, that many features of the biological world could be ascribed to the elegant principle of natural selection.

Darwin's idea of natural selection makes people uncomfortable because it reverses the direction of tradition.

Evolution thus is merely contingent on certain processes articulated by Darwin: variation and selection.

As Darwin himself was at pains to point out, natural selection is all about differential survival within species, not between them.

Darwin recognized the fact that paleontology then seemed to provide evidence against rather for evolution in general or the gradual origin of taxonomic categories in particular.

All scientists agree that evolution has occurred - that all life comes from a common ancestry, that there has been extinction, and that new taxa, new biological groups, have arisen. The question is, is natural selection enough to explain evolution? Is it the driver of evolution?

If we turn to palaeontology to tell us about our biological evolution it is to prehistory that we look for evidence of the evolution of specifically human patterns of behaviour.

In the last century, as we learned more about genes, we were able to devise ways of accelerating evolution.