(Original post by yomomalomo)
No, sorry tarzooni, you do not seem to understand speciation very well. We did not, as humans, come from a single pair of two ancestor apes whose children multiplied solely amongst themselves. That is why it is wrong. our ancestors moved in groups much like we do today. Being disconnected environmentally from their relatives, e.g. if a group of 30 cross a river while another prefer to stay on the other side, then the group will begin to diverge, genetically from the others (if they stay on the other side). On the other side of the river is an environment with different selective pressures, because of this, the apes evolve to cope with them. Again, as the groups are split any differences that occur amongst them will stay separate rather than mix, because there is no mating between them.
When a child is born with a successful genetic mutation, when it grows up it will mate with an ape-humanoid of different parents. Its successful mutation will be present in some of their children, these children will survive and continue to procreate, again not amongst themselves, passing their successful genetic material onwards.
Now you may ask why the child with the successful mutation not mate with its sister who is born one year later, for example. First of all, it is not much more likely that its sister will have the same successful genetic mutation, however, it is very likely that she will have the same rest of his genes. This means she will have the same genetic flaws, or things which are not so successful. Because of this, if they interbreed, their offspring will have a much greater chance of having bad phenotypes, because their will be a lack of variant dominant genes to mask the recessive ones. This makes it less likely the offspring will survive - the animals die out. However, if the child(A) with the successful gene mutation mates with the child of different parents (B), then there is nearly the same, but maybe slightly slightly less chance that their offspring will have the successful genetic mutation that A has. Instead, there is an increased chance of their being any successful mutation that occurred in B occurring in the offspring and there is also a massively decreased chance that any of the recessive genes in A) will be shown in the offspring.
Basically, incest reduces net chance for successful mutations to occur in offspring, while increasing with chance of recessive genes showing themselves. It is an evolutionary fail and that is why so many plants and animals have adapted so as to reduce the chance of it ever happening. Just look at most plants and you will see that the anther is very far from the same plants ovary so as not to self-fertilise. Some plants go further, like apple trees, having female and male versions of themselves so as not to reuse the same genetic material. In animals it is only more prominent as there have been studies showing that the body odour of close relatives is incredibly off puting to animals, while the odour of unrelated animals is alluring. This is actually based in the rhinocephalon or nose-brain which is an extremely archaic part of the brain - one of the first parts. It is such an unsuccessful thing to do that it is actually hard-wired in mine and your brains, along with numerous other animals, to not do it.
That is why it is highly unlikely that there were two people or proto-humans that were made or evolved to that point and then purely by themselves populated the whole world.