"An earlier generation of anthropologists tried to explain face form in the Horn of Africa as the result of admixture from hypothetical “wandering Caucasoids,” (Adams, 1967, 1979; MacGaffey, 1966; Seligman, 1913, 1915, 1934), but that explanation founders on the paradox of why that supposedly potent “Caucasoid” people contributed a dominant quantity of genes for nose and face form but none for skin color or limb proportions. It makes far better sense to regard the adaptively significant features seen in the Horn of Africa as solely an in situ response on the part of separate adaptive traits to the selective forces present in the hot dry tropics of eastern Africa. From the observation that 12,000 years was not a long enough period of time to produce any noticeable variation in pigment by latitude in the New World and that 50,000 years has been barely long enough to produce the beginnings of a gradation in Australia (Brace, 1993a), one would have to argue that the inhabitants of the Upper Nile and the East Horn of Africa have been equatorial for many tens of thousands of years."
Clines and Clusters Versus “Race:” A Test in Ancient Egypt...36:1-31 (1993).