We may need to consult Denis Venema here. As I understand it, the human population displays “incomplete lineage sorting” vis a vis ape ancestors.
What that means is that the human population was never in one place long enough to agree on one complete set of genes from our ancestors: some populations have more orang utan or chimp genes than another. As far as I can see that suggests a picture of small populations scattering, occasionally cross-breeding, hybridising with different variant populations (or Neanderthals) etc.
Now imagine human speciation occurring in that kind of scenario, and there need never have been a “core population” all together at one place or time. So that’s why it’s a bit tricky even to define our “humanity” in biological terms - theology probably gives us a better handle on it.