What is it called when a part of a population migrates repeatedly to another population?

Select the appropriate option for the given figure.

In forming the theory of evolution by natural selection,Darwin was greatly influenced by

Given below are two statements regarding evolution.
Statement-$I$: Natural selection is the establishment of a phenotypic trait in changing environmental conditions.
Statement-$II$: Natural selection encourages those genes or traits that ensure highest degree of adaptive efficiency between population and its environment.
In the light of above statements, choose the most appropriate answer from the options given below.

Darwin,in his 'Natural Selection Theory',did not believe in any role of which one of the following in organic evolution?

Discuss natural selection and artificial selection. What are the implications of the latter on the process of evolution?