Variation in gene frequencies within populations can occur by chance rather than by natural selection. This is referred to as

Statement-$I$: The fitness according to Darwin,refers ultimately and only to reproductive fitness.
Statement-$II$: Those who are better fit in the environment leave less progeny than others.

'Essay on the Principle of Population' was published by

In natural selection, more individuals acquire value other than the mean character value, which indicates . . . . . . .

According to the Neo-Darwinian theory,which of the following is responsible for the origin of new species?

The peppered moth $(Biston \text{ } betularia)$, the black-coloured form became dominant over the light-coloured form of moth in England during the industrial revolution. This is an example of