Scientific Adam and Eve

[Alex K]

I read an article that I linked in a different post on this thread that its plausible that they could have lived at the same time.

Given the ranges, it seems unlikely - and there is no logical necessity that they should have. But even if they had lived at the same time, they don't even need to have met.

And please correct me if I am wrong, but I thought that speciation was the point where an evolutionary line did branch out on its own? Wouldn't this be a clear distinction in the space time continuum? ok, I don't know what that last part was supposed to mean, I just want to sound smart too :/

I am nothing close to a speciation expert, but if the branching out happened because a small subpopulation suddenly became isolated from the rest, then I'd say you have a clear cut date. If it is sympatric, and a sub-population drifts away from the rest while still living in the same place (but probably occupying a different ecological niche) it might be more subtle, with cross-breeding fertility between the two groups going down continuously. Of course at some point may be the last time when members of the two groups interbreed, but at that point, the groups might already be quite separate. But again, IANAB.

Why are mules for example sterile? I believe the same went for Ligers, which are real! Does evolution have a safety mechanism that keeps us equal but separate?

Darwin already writes about this in "Origin" taken from his experiments with plants. I suppose fertility simply goes down when inbreeding because harmful mutations in one set of chromosomes can not be compensated by a new intact second set from the outside any more, and there will be less and less viable embryos produced.