Re: Were Neanderthals another species of Homo Sapiens?

On 12/8/24 12:04 PM, RonO wrote:

https://academic.oup.com/evolinnean/advance-article/doi/10.1093/evolinnean/kzae033/7900502?login=false
 Open access.
 Two anthropologists are making the case that Neanderthals were different enough to be considered to be a different species from modern humans.
 We could obviously interbreed, but there were physical and genetic differences.  We are around as different from Neanderthal in our DNA sequence as Bos taurus (western domestic cattle) and Bos indicus (Asian domestic castle).  Taurus and indicus can freely interbreed, but the Auroch populations that they were derived from had been genetically separated for over half a million years.  This is about the same amount of time that Neanderthals and Modern humans have been estimated to have been separated.
 The physical differences are mainly due to Neanderthal having to survive multiple 100,000 year long glacial periods.  Neanderthal retain many features associated with Homo erectus, but they are more robust with much larger nasal openings in their skull.  The overall shape of the skull is closer to H. erectus than to modern humans if you factor in the increased brain size.  This paper notes that the Neanderthal retained the ribs that flare out in H. erectus and apes, but constrict in modern humans to give us the hour glass figure instead of the fire hydrant build musculature.  Neanderthal internal organs could be larger and adapted to do who-knows-what.
 Modern humans were eventually more gracile and slighter of build than Neanderthals, but Cro-Magnon were very robust individuals that were eventually replaced by what currently passes for modern humans.  I recall being shocked the first time I saw a comparison of Cro-Magnon, Neanderthal and modern human teeth.  Neanderthal and Cro-Magnon teeth were comparable in size, but larger than modern human teeth.  Cro-Magnon had a cranial capacity about equivalent to Neanderthal, but modern humans have less cranial capacity (smaller brains).  So what physical differences were really different between modern humans and Neanderthal when they first met?
 My take is that we should just go by DNA difference, because the other measures would be subjective.  We know that we can't go by DNA differences in all cases because you have instant speciation in cases like tetraploids.  You have cases like arboreal anteaters that were thought to be closely related subspecies, but they had DNA differences indicating separation for millions of years.  So what can be made of phenotypic similarities and differences?
 If you claim that different species can still interbreed and exchange genetic information you might as well just give up on the species term and start identifying populations that are genetically isolated and have been for some extended period of time.  You would have to develop some quantifiable measure for measuring the amount of genetic exchange that may have occurred over the period that the populations were not interbreeding on a regular basis, and develop levels of genetic isolation that would warrant calling the populations some different species name.  You would have some DNA measure to determine when a population was different enough from the ancestral population to call it something else.  It would likely be some point where loss of the genetic information due to extinction would be a major loss of genetic variation from the existing related populations that make up the current "specie".

The question is whether their genotypes remain highly divergent in sympatry. In that case, even if they're interbreeding, it isn't enough to merge the gene pools, and that would make them separate species even if there's some introgression.