and chances are again much higher that whoever it picks will have at least one of those same deleterious recessives. It can happen that, purely because of bad luck, those people with the normal allele for a given gene fail to pass it on, and everyone in the population ends up with the deleterious recessive allele. Chances of this arent high for a specific gene,......
Now picture having a baby with your sibling or parent (which is what would presumably have to happen if humans were trying to rebuild from two individuals). You got your deleterious recessives from your parents. So did your sibling. So if you produce a baby with one of them the chances are much higher that the baby will get 2 deleterious recessives on the same gene.
If the baby survives and grows up it will have to find someone to have a baby with, and chances are again much higher that whoever it picks will have at least one of those same deleterious recessives. It can happen that, purely because of bad luck, those people with the normal allele for a given gene fail to pass it on, and everyone in the population ends up with the deleterious recessive allele. Chances of this aren't high for a specific gene, but the chances are pretty good that out of all the genes in the genome, this will happen to one or two of them.
Now that being said, I don't personally think it's true that it would be *impossible* to repopulate the planet starting from two people. It would depend on which two people you started with, and to what extent you tried to encourage breeding among the least related people after that. The horror stories you often hear about inbreeding producing complete infertility in a few generations generally apply to experiments with farm animals in which the siblings are bred to each other, and then the siblings of the next generation are bred to each other (rather than to their cousins), and then the siblings of the next generation are bred to each other (rather than to their second cousins), and so forth. So the inbreeding is artificially reinforced.
You could repopulate the world with two people assuming one is male and one female. Most likely populations with distinctive traits are the result of small groups breeding for many generations.
The problem is usually that recessive genetic diseases would appear. Genetic diseases that are recessive require both parents to carry the same defective gene, and if everyone has identical or nearly identical genes there is a greater chance that genetic diseases will appear. There are many examples of genetic disorders that are found in only one population. The Irish, for example, have a genetic disorder that results in an overload of iron in the blood. It is potentially fatal, but not for many years. If those 2 people ( Adam and Eve) were lucky and didn't have any fatal recessive genes they could eventually repopulate the earth.
I also think it is impossible right now. It's like making a copy of a copy of a copy. It degrades, meaning as soon as inbreeding happens you get a lot of flaws. Now the first two persons to live would have been perfect and flawless. So it could have happened.
To expand on what others have said: The inbreeding would cause birth defects and everyone would have the same weaknesses to diseases so if one person got sick with a bad disease everyone would die.
Inbreeding because DNA is so similar. MUTANTS!
