>>Given that childs born from incestuous relationships as a far greater chances of having malformations or other handicaps, what are the odds that the humans race survived in that context?
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>It survived so far as far as I know <g>

Or the premise is just plain wrong?

Just look at the American Americans. Their origins were traced to just five families who once crossed the Bering strait when it was frozen. Their genetic pool was very shallow - which explains why they were so susceptible to all the diseases brought by whites. If one of them was, they pretty much all were. They were decimated.

While the opposite didn't happen - the Europeans were far more resilient, being the offspring of peoples who have survived all sorts of diseases brought by just about any army from anywhere in the Old World (counting from Mongolia to India to Sahara to Ireland to North Sea). So they inherited resistance to diseases they knew, and they didn't catch much of anything on the new continent.

Now if reduction of a population to five families (I've also found "five mothers") gets you into such trouble, how far does inbreeding within a single family get you?

I know of a case of a single place where they just kept marrying their children across the village and not to anyone outside. They were already under Academy of Science's scrutiny for the abnormally high percentage of mental cases (and that's based on known cases - those they managed to keep locked in cellars and attics weren't counted anywhere). One hears a lot when picking up a local policeman hitchhiking home (the place had no cops of their own - they had to have a few assigned).