Allopatric speciation is due to

The correct meaning of natural selection is

Organisms that possess favorable variations are considered to be:

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.

According to $Darwin$,fitness refers to .........

The concept that "Population tends to increase geometrically while food supply increases arithmetically" was put forward by: