Natural selection: Heritable variations that enable survival of the fittest will leave greater number of progeny. Natural selection can have following three effects:
a. Stabilisation: Larger number of individuals acquire mean character value so peak gets higher and narrower.
b. Directional change: Large number of individuals acquire value other than mean character value so peak shifts in one direction.
c. Disruption: Large number of individuals acquire peripheral character values at both ends of the distribution curve and hence 2 peaks are formed.