Before we can say how different races formed, we must first find what constitutes a race, and then see a little about how genetics operates. During the 1960's, many people began to try to eliminate racism and its prejudices. The A.A.A.S. convened a conference, attended by many experts in the field. Noted taxonomist Ernst Mayr said,
"... But if we look at some recent textbooks on physical anthropology, we find that in one textbook they recognize five human races, in the next textbook they recognize sixty-five human races. Races there are; how to delimit them, how to draw the line between them is not only difficult, it is impossible." (Ernst Mayr, in Science and the Concept of Race, American Association for the Advancement of Science, New York: Columbia University Press, 1968, page 16).
Speaking at the same conference, Bentley Glass said,
"Races are subdivisions of a species. There is no real distinction between races, in the anthropological or zoological sense, and subspecies. Races (or subspecies) are always separated from each other in space or time. In other words, contemporaneous races or subspecies always are separated from each other geographically." (Bentley Glass, Science and the Concept of Race, page88.)
But how did different races form in the first place, if there was originally a large group of similar people? It's a well-known fact that if a few individuals from some much larger group are isolated, the variety within the small group's gene-pool is reduced. Some genes that are subordinate in most members of the original large group will be completely missing in the smaller group. Therefore, later generations from the small group, if left in isolation, will never develop some of the diversity of the original large group. Glass called this the "Founder's Effect," and explained:
"Small populations therefore come to differ radically in their gene frequencies from the populations of their origin ... Whenever a new colony is established by a very few individuals, it cannot be fully and proportionately representative of the gene pool from which it is drawn." (Glass, op.cit., page 91).
Darker or lighter skin is not caused directly by a person's being more or less exposed to intense sunlight. It's caused by the amount of a pigment caled melanin, and this is controlled by genetic factors. People with more melanin have darker skin, and this helps them be more resistent to skin cancers from intense sunlight. Natural selection tends to promote dark skin for those living in hot areas. On the other hand, people with less melanin can utilize the sun's rays to better produce vitamin D, which helps them to avoid rickets, and is needed in polar lattitudes. Thus natural selection tends to concentrate light-skinned people in the polar regions. In both cases, the lack of disease (cancer or rickets) selectively enhances people of certain color.
Noah and his family almost certainly had medium brown skin, and had a full complement of genes that included all that today's peoples have. But his descendants became isolated groups as they spread over the world. Each isolated group must have had fewer of certain recessive genes than some of the other groups; in time these became completely absent, so all members of that group would share an appearance different from other groups. In other words, they would become a different race.
This effect became especially enhanced after the dispersion following the Tower of Babel. At that time, God caused a confusion of languages and deliberate dispersion to far-off places for the various small groups. This isolation quickly caused differentiation of groups and proliferation of races.
We could formulate two general rules for formation or dissolution of races, as follows:
1. If a small portion of an initially broad population is isolated for many generations, then a "race" is produced, because their gene pool is reduced in variety. Members of this race share common characteristics that are different from those of descendants of some different isolated group, whose gene pool has a different makeup.
2. Conversely, if two "races" that had previously been isolated for many generations are brought together and then intermarry, later members of this newly merged broader society lose the sharp differences of the original races, and get characteristics that cover a wider range of shared average appearances. Their new gene pool shares from both original races.
http://www.rae.org/bits18.htm
: Sorry friend, but when you claim that apes passed on genes they didn't even carry, then you're the last person to question the descendants of Noah's sons! If apes can breed human descendants, then Noah can breed anything!! So your question is contradictory and therefore bogus. ;-)