I haven't looked into this much, but I'm sure I've heard that it only took about 20,000 years for skin color to change from dark to light (Arican to N.European). But that is with some selection pressures such as the vitamin D/Folic acid paradox. Maybe 850,000 yr. is right, but are there ever no selection pressures?
~Sam

Pyrolysis creates reduced carbon! ...Time for the next step in our evolutionary symbiosis with fire.