natural selection

Industrial melanism in the peppered moth, first noticed by English geneticist Henry Kettlewell. He observed that whereas in rural areas peppered moths were light in colour to camouflage them against the lichens, in industrial areas where the tree trunks were dirtied with soot, peppered moths were darker. Natural selection favoured the darker mutation in industrial areas because it offered better camouflage there, so it had become widespread, whereas in rural areas the darker mutant was highly visible against the lighter tree trunks and so was easy prey to insect feeders.

Process by which gene frequencies in a population change through certain individuals producing more descendants than others because they are better able to survive and reproduce in their environment. The accumulated effect of natural selection is to produce adaptations such as the insulating coat of a polar bear or the spadelike forelimbs of a mole. The process is slow, relying firstly on random variation in the genes of an organism being produced by mutation and secondly on the genetic recombination of sexual reproduction. It was recognized by English naturalists Charles Darwin and Alfred Russel Wallace as the main process driving evolution.

Natural selection results in evolution in a way that was described by Charles Darwin: individual organisms within a particular species may show a wide range of variation because of differences in their genes; predation, disease, and competition cause individuals to die; individuals with characteristics most suited to the environment are more likely to survive and breed successfully; and the genes which have enabled these individuals to survive are then passed on to the next generation, and if the environment is changing, the result is that some genes are more abundant in the next generation and the organism has evolved.

Natural selection usually takes place over many years, but in fast-breeding organisms it can occur rapidly, for example the spread of antibiotic resistance in some bacteria.