My understanding of this is that we are, pretty much, aside from some far south African communities, part Neandethal. Gene migration spread back to Africa once we, as a selection of species, realised it was possible.
I, for one, welcome our slug-human hybrid overlords.
Also banana-human hybrids, which is the most common claim as to shared DNA I have heard. I am not totally convinced.*
Wait! Banana slugs exist. We are doomed.
* this is satire. I have never heard this claim.
Imagine this as a thought exercise. A grouping of creatures travel down an evolutionary path, mixing with others of their ilk nearby, but generally (unless we get to a ring species) they are essentially the same species. They keep mixing, and one reason species differentiate is to ensure like is attracted to like.*
Now it’s possible the speicies is separated, and some group is isolated on a tropical island subject to such intense environmental pressures that they evolve to be different and present as a different species - or maybe they end up with one member duplicating a chromosome and maange to continue and procreate such that this becomes a characteritic of the species.
Meanwhile, back at the ranch, the existing original species is so spread out that some of them - on the shore near the island - are more related to this new species than they are to the distant members of their species.
But generally - no. The species is a group that evolved together, choosing to mate with members who displayed the same characteristics that ensured survival. This selection for shared characteristics ensures the coherence of the species.
*There’s a concept off “differentiation”. One speculation is that sapiens sapiens has nice chins to distinguish from neaderthal and others - people are attracted to what’s the norm for them, so something that distinguishes themselves from neighbouring subspecies ensures that mating attraction etc. is more “optimal” - also a species survival mechanism. Also in theory why bird species develop distinctive coloration between species - so they know they are chasing compatible mates…
Thank you!
Thank you so much for that answer!
Some very hekpful answers and thank you! I am also satisfied having read the brilliant article - Genealogical Perspectives On The Species Problem
David A Baum and Kerry L Shaw
It argues focusing on the genealogical histories of genes rather than measuring relatedness in terms of recency of common organismic descent.
Yeah, but the common ancestor for a species will not have been a member of that species, because speciation happens to populations (maybe not for organisms that reproduce asexually, parthenogenetically etc - speciation could begin with a single individual in those cases)