|
|
|
Neo-Darwinism Part 3
There are various reasons why gene-frequencies might alter: immigration, emigration, random drift, and natural selection. Immigration, emigration, and random drift are not of much interest from the point of view of adaptation, although they may be quite important in practice. It is natural selection that accounts for the perfection of adaptation, for the complex functional organisation of life, and for such progressive qualities as evolution may (controversially) exhibit. Genes in bodies exert an influence on the development of those bodies. Some bodies are better at surviving and reproducing than others. Bodies that are good at surviving and reproducing will tend to contribute more genes to the gene pools of the future than bodies that are bad at surviving and reproducing: genes that tend to make good bodies will come to predominate in gene pools. Natural selection is the differential survival and differential reproductive success of bodies: it is important because of its consequences for the differential survival of genes in gene pools.
Not all selective deaths lead to evolutionary change. On the contrary, much natural selection is so-called stabilizing selection, removing genes from the gene pool that tend to cause deviation from an already optimal form. However, when environmental conditions change, either through natural catastrophe or through evolutionary improvement of other creatures (predators, prey, parasites, and so on), selection may lead to evolutionary change.