Which of the following scientists believed in the concept of natural selection like Darwin?

Genetic drift operates in

The ultimate source of organic evolution is

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:

The natural selection that acts against change in the form and keeps the population constant through time is

Natural selection in which more individuals acquire peripheral character values at both ends of the distribution curve is: