One could easily argue that incest is something that happens more often within more advanced societies (nobles marrying each other, severely increasing incestuous relationships), so it actually makes sense that it didn't happen very often in the ancient days where people would marry people from other groups and therefore deformations were far less common.

I doubt one could say it 'never happened' though, I am sure there must have been plenty of deformed people (that had a bad chance of surviving) and honestly there's a fossil record that back that up.

Also, don't forget that certain reproduction errors that we call for example the Down Syndrome do have their own origin as well. The fact that in modern days chances are incredibly high that you'd get deformed kids when having incestuous relationships doesn't mean it used to be the same in ancient days.

Add to that the mere fact that we're globally mixing our genes for quite some time too now, meaning people will inevitably also have more genetic information in common.

It still doesn't mean we're doomed to end up only being able to reproduce people with the Down Syndrome either though. ( Isolation of groups and merging them later on having evolved independently for example will be good for the gene pool and many other workings of evolution will keep larger groups healthy for a very long time. )



Technically this is not true, as this is only valid for individual atoms, not groups of atoms, nor entire beings from what I understand.

When you look at this from the probability perspective of where an atom will be at any given time, this doesn't mean our body is time traveling all that time being in different places. Of course, when you look at this from a multi-dimensional perspective, it could very well be true for entire beings as well... but that's rather a stretch of the evidence as far as I can tell.