Go look deeper into how population dynamics works-- it's never just a single pair.<quoted text>
A specific population can't be sustained by just a single pair. That much is true. But I'm not interested in sustaining. What interests me is how the process starts.
It would seem that you would need two creatures that have reached sexual maturity at the same chronological point in time, in the same location, that they would successfully mate and produce offspring that could also repeat this process. That's what interests me. Where or how do these two biological creatures come into contact at the right place, at the right time, with the optimum health needed to reproduce and carry on?
Species comes from populations and groups of individuals. By definition 'species' represents a group of individuals who are fertile with one another, and generally speaking, in contact pretty much all the time-- or at the very least, in the same general area.
If evolution is true-- and all the facts and information say it is-- then there never was a single pair of "first humans".
Any more than you can draw distinct lines in a rainbow, to separate the colors-- oh, you **can** but it's purely arbitrary. The colors gradually fade from red to deep ultra-violet, without any steps in-between.
Evolution of species is like that: gradual, tiny baby-steps from one minor change to the next.
Such that, across any 10 generations, you could still likely (using a mythical time-machine) take a random pair, and get viable offspring.
The more you separate the generations, though? The more likelihood of a genetic defect, and non-viable offspring.
Eventually, with enough generational separation, that the pair won't even be interested in trying to breed, let alone be capable of it.
There's no single event that separates the 1000-generation apart individuals-- there's literally hundreds of millions (or more) of microscopic steps.
All of which add up to: a different species. Even though they probably look very much the same on the outside.