The idea of "survival of the fittest" was given by

When a change in the gene frequency of population occurs by chance,it is called . . . . . .

Name the type of natural selection depicted in the given diagram (Type $I$,Type $II$ and Type $III$).

Given below are the two statements.
Statement $I$: Directional isolation favours the intermediate forms and eliminates both phenotypic extremes.
Statement $II$: In directional isolation,more individuals acquire a value other than the mean character value.
In the light of the above statements,choose the correct answer from the options given below:

Species that are separated by geographical barriers are called ........

The correct meaning of natural selection is