Statistically , sickle cell anemia rides along with immunity from malaria. The slave trade to the new world has often been tied to the fact that early settlers who brought indentured servants from their own homelands saw that mpot of these died frommalaria. SO, whe it was discovered that Many AFricans had immunity to malaria (falciparum included0, then slavery became a way of life for the latitudes south of where the Anapholes didnt winter over. In New ENgland it was till a society of indentured servants who became greed men after a contractual obligation and (often_) some money changed hands.
In the area south of the MAson Dixon line , (The farthest N advance of falciparum malaria was about Richmond or DC at the most).
All those definitions and "tests" of subspeciation are just bullshit based upon homeranges of organisms. Species can diverge based upon geographic isolation until species are confidently assigned. EVEN so, there are often miscalls, like the red wolves of the AFar, or BArren ground Grizzlies, Kodiak Island Grizzlies, Alaskan Brown Grizzlies, and Mountain Grizzlies
I like Thomas take on the globalization of our species.
I suppose if you really need to insert humans within a mechanistic ( and quite artificial) Creationist classification ystem, I cant top you, its just that Id get a better feel of the actual "Species problem" and the concepts of phylogenetic species v geological species.
EO Wilson has a really good (And approachable) discussion of the species v subspeies v population controversy.