And then consider the sort of image which Sir Mortimer Wheeler called a "priest/king type" found in Indus Valley sites:
Notice any sort of a resemblence?
The genetic studies so far have been based on mtDNA, which is almost purely matrilineal and probably not a good enough molecular clock for the purpose. (A nuclear DNA study would be nice, if a good-enough specimen is ever found.) Also, as this survey article indicates, the anatomical differences are far more pronounced in Europe than they are elsewhere, especially the Near East. There thus may have been a local "species gap" that didn't exist everywhere at once. The situation would have resembled modern ring species in birds and salamanders.