Effects of different forms of selection on evolution

Selection pressure:

• change in an environment stimulating evolution

Stabilising selection:

• preserves the average phenotype (phenotypes around the mean) of a population by favouring average individuals, in other words, selection against the extreme phenotypes 
• tends to occur where the environmental conditions are constant over long periods of time

Directional selection:

• changes the phenotypes of a population by favouring phenotypes that vary…