Natural selection and [[1]] have together led to the formation of a population that cannot reproduce with the original one.

Natural selection and genetic drift have together led to the formation of a population that cannot reproduce with the original one.

The survival of a species depends on its environment. If the newly generated species is in any way better than the older one, it will flourish. 

Natural selection and genetic drift together lead to the formation of new species due to mutations, differences in alleles, and reproductive isolation. This causes incompatibility between the two populations as they cannot reproduce with one another.