According to wikipedia, "comparisons between known skin pigmentation genes in chimpanzees and modern Africans show that dark skin evolved along with the loss of body hair about 1.2 million years ago and is the ancestral state of all humans." This is several million years after after the time estimated for the last common human-chimpanzee ancestor, but at least 1 million years before the emergence of Homo Sapiens. This suggests that the earliest species in _Homo_ may have had lighter skin, but that the advantageous genes for dark skin were universal by the time of the first true humans.