Malaria is a blood parasite carrier by mosquitos. Malarial parasites cannot infect sickle cells. Taxonomy is an inexact science, there is debate over how to divide living organisms into species. The environment of a species and its adaptation to that environment. They are separated by a barrier which reduces gene flow.
Differences accumulate in gene frequencies.
The difference is also increased if macromutations occur. After sufficient accumulation of genetic differences, the two populations become distinct species. Radiations caused by Punctuated Equilibrium 1. When a niche is empty of competing species. When environmental change causes mass extinctions which empties niches of competing species.