Where do you draw the line that you get three, let alone three that are distinct? Where do you shoehorn people from New Guinea and Australia - "Negroid" because of the color of their skin? They are closer to both Asians and Caucasians than Africans.I guess it begs the question of how humanity developed into three distinct races: Caucasoid, Negroid and Mongoloid. Don’t you think there should be some residual traces in each race? Why are they so different/distinct from each other? You said that black skin is more protected from the sun but then why are black skinned people more susceptible to sunburn? Then too, there are several levels of black skinned people in Africa. Shouldn’t they all be the same?
Why are the races so distinct from each other? Genetically they are not, we are a very homologous species as far as DNA similarity goes, but there are obvious differences that are mostly “skin deep” as it were.
Why do you think a black person in Africa who goes half naked every day is more susceptible to sunburn than an Irish red head who freckles and burns in 15 minutes? Someone told you that once and you accept it without any more evidence, despite any and all other evidence?
There is such a thing as genetic variation, and there is a lot more of it in Africa than elsewhere. Why would you suppose they would all be the same any more than that your average Norwegian and your average Italian would be same in amount of melanin content in the skin?
So what mechanism do YOU propose is responsible for population differences?
Where do you draw the line that you get three, let alone three that are distinct? Where do you shoehorn people from New Guinea and Australia - "Negroid" because of the color of their skin? They are closer to both Asians and Caucasians than Africans.Today we know that Europeans are mostly descended of Ice Age survivors who holed up in three "refugia" (places not turned to desert or covered with ice sheets). That separation lasted from about 35,000 years ago to 15,000 years ago.
At least one subgroup broke off and moved to America about the peak of the ice some 20,000 years ago ~ and their descendants are still around ~ with their own unique identifying DNA sequence.
East Asians are descended from several different populations that holed up in Eastern "refugia". Further, even though Chinese and Europeans are the same people separated by about 35,000 years, they did swap girls across the vastness of Asia back during the Ice Age so we've all got 5% of each other's otherwise unique DNA sequences. The Chinese also divided into two groups, one of which is better known as the Ainu (who are closely related to the Jomon and Emeshi populations in Japan in earlier times).
The earliest people to leave the European refugia in the West went straight North to Norway and became genetically isolated from other Europeans until about 800 AD. Parts of that population moved on East over the top of Scandinavia and met up with other Europeans coming in from the South.
I think that gives you 5 distinctive "European races".
Then there are the people from the Middle East and North Africa who also moved into Europe, etc. over time.
The people in Africa are otherwise identifiably members of 13 other haplogroups! There the reasons for divergence and isolation had to do with the abominable climate in most of Africa, and physical barriers that made movement from one part to the other quite difficult until modern times 75,000 years later after the ancestors of the Europeans and Chinese had gone North!
There are mixed populations throughout South Asia ~ Indians, for example ALL (means 100%) have genes from both Persian and Andaman Islander type populations. The vast array of facial types and colors have arisen subsequent to that mixing.
All in all, as far as older definitions of "race" go, we probably have 40 or 50 of those!