Directional Selection

The phenotype of an individual is an observable characteristic of that individual. This may be anatomical, physiological, behavioural or biochemical.In any population, individuals possess a variety of phenotypes, but most individuals will have an average phenotype while fewer will have phenotypes to the left or to the right of the mean.If the environment changes and the new conditions favour the individuals to one side of the mean, the individuals will contribute more alleles to the gene pool of the population as the result of their reproductive success.Over time, the mean will move in the direction of those individual characteristics.If selection favours one extreme it is called directional selection.