>> But... but... 6+ billion people descended from Adam and Eve! <<
Even according to evolutionary biologists, all humans *are* descended from the same mother, only about 20,000 years ago!
Further, genetic ailments are caused by mutations. From a creationist point of view, Adam and Eve would have had no mutations.
Correct me if I'm wrong, but I think you have taken the erroneous approximations based on mitochondrial nucleic acid material.
THE EVE CONTROVERSY
The chance that all humans today are descended from a single couple only 200,000 years or less than 10,000 generations ago or so [Fitch p251] and still have the nuclear diversity which they display today is completely impossible, for hundreds of thousands of generations seem to be required [Wright p150] at least, so the above or something like it is essential. Mitochondrial DNA is poor at predicting the age of a genetic line. Low-diversity mitochondrial lineages, typically disregarded as important from a conservation standpoint, might sometimes correspond to recently selected, well-adapted haplotypes to be preserved [Bazin]. It has been estimated from analysis of the HLA immune genetic complex that human populations have never sunk down below a 50 or 100 thousand population [Ayala & Escalnte, et al1995, p205], let alone a single individual. Evidence from recessive disorders of the apolipoprotein C-II activator of lipoprotein lipase Japanese and Caucasian progenitors must have diverged two million years ago [Ayala & Escalante et al, p206]. We have seen one hundred human generations come and go with very little change in appearance, at least, judging from ancient portraits. To imprint a trivial nuclear genetic difference on a population requires large numbers of deaths or failures to reproduce. Humans have not had large numbers until recently, nor short life spans, nor have they ever had large numbers of progeny, say 100 or 200 to a woman. Trivial traits and mere differences in appearance take a long, long time to monopolize a population even when there is mild active sexual or other selection for them. Humans have a very large number of trivial differences in appearance and even a fair number of fundamental differences in organ design and enzyme systems. Humans reproduce largely by visual clues so that there is strong pressure to reject even small differences in appearance, especially in primitive societies. Humans have considerable individual and family choice in mate selection.
Non-gene sequences, which are subjected to zero selective pressure, show considerable per cent variation across the world [king]. In addition to all of the above, there is a definite tendency toward inbreeding within their villages and hierarchies, not from any obvious physiological bars, but only from cultural bars. Barring a drastic unknown difference in any of the above parameters in ancient times, it is safe to say that no single family could possibly have been responsible for all the present day nuclear gene variety in only 200,000 years, or even 2,000,000 years. Never mind variety, just splitting the races apart in such a time is impossible. It is thought to have taken over 12,000 years just to occupy the South American continent. Australian aborigines entered Australia 50,000 years ago [Bowler], and there is evidence that Australia was colonized by modern humans at least 50,000 or 60,000 years ago and these humans are more genetically different from Africans than any other groups are from each other. Obviously those aborigines split off from other humans then and thus left only 150,000 years or less to reach their diversity, given a single couple origin hypothesis.
When human mitochondria swept across the world, but probably not from Africa (fossils show no sure evidence of modern humans in Africa [Thorne] ) and an out of Africa hypothesis is far from proven [Dennell], they would have had no problem picking up from or imparting traits to the "people" they met along the way, and surely must have. Fonda makes a persuasive case that humans arose in Eurasia and hybridized with Homo erectus and other hominids there, part of his argument being that Eurasians are more closely related to each other than to Africans, that artifacts showed up there first, and that Africans have more diversity than Eurasians and thus were presumably hybridized with resident populations.
He has reviewed more recent genetic data. The Mmacrohaplogroups, M and N, have been claimed to be of African origin, but the latest research shows that M is Asian (Indian). Further, the nuclear DNA affinities of Indians are to south east Asia, and the south east Asians are the most divergent from Africans of any people on earth. That is in accordance with Fonda’s theory, because Asian and African erectus were separated for nearly two million years, allowing much more divergence than the 50 or 60 thousand that recent out of Africa populations would have had for diversity to arise and contradictory to the out of Africa hypothesis. There is a Eurasian-Hss component to both Africans and Australian DNA, and that is about the same, but the Homo erectus derived portions of the African and Australian DNA are very divergent, because the Asian and African Homo erectus components had 2 million years to diverge. Moreover, he notes that the fossil mtDNA inclusion on chromosome 11 of the nuclear DNA is very ancient, and its geographic distribution shows that it was of north east Asian origin. Since it is clearly antecedent to LM3 and all the other lineages of Australian mtDNA (except the Kow Swamp type that came in through New Guinea during the most recent ice age) belong to macro-N, he contends that N is also of archaic Asian provenance. Fonda has presented a very elaborate analysis of Australian settlement and suggests that Australia was originally settled by central Asian migrants (who later became Europeans), and then were supplanted by the current aborigines, who had been hybridized with southeast Asian homo erectus.