Why do adaptations occur?

Give scientific reasons: Genetic drift is much more likely to change allele frequencies in a small population rather than a large population.

In the diagrammatic representation of the operation of natural selection,two peaks are formed. This condition shows the effect of . . . . . . .

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:

When we say 'survival of the fittest',does it mean that $(a)$ those which are fit only survive,or $(b)$ those that survive are called fit? Comment.

State and explain any three factors affecting allele frequency in populations.