Geologist Marcus Ross at Liberty University responds to “Did the prehistoric Denisovans cross Wallace’s Line?”, wherein it was noted that
We don’t know very much about the Denisovans, but anthropologists have been wisely reluctant to classify them as a separate species (consider, for example, the Flores man debacle). So the media release quoted above is careful in its choice of words; the Denisovans are a “line of the human family tree” (so is your family, and mine) or “ancient human relatives.”
He writes to say,
I think that the paleoanthropology community will be slow to reduce the number of purported species within Homo. However, the physical diversity in the skulls from Dmanisi is really wild. Lordkipanidze et al. are convinced that the new cranium and jaw (Skull 5) still reside within Homo. If they’re right, then the argument that H. erectus can absorb H. ergaster, and H. georgicus is very strong, and has substantial implications for knocking off H. habilis and H. rudofensis as well. From five species down to one. Neat trick, and would be fine by me.
So if Lordkipanidze et al. are right that the 5 skulls from Dmanisi are all the same species of Homo (most likely erectus), then the fact that they have 5 quite distinct skulls from one location has significant bearing on how physically diverse early Homo was. As they note, many of the other “species” of Homo come from isolated discoveries, where it is tempting to see the discovery as more unique than what it is. They make a very interesting case for pruning the tree of Homo.
My sense is that Darwin’s theory would be a priori more plausible if there were a number of dumb, failed human species around at any given time, and ours just happened to make it to the top.
If there was never any more than one human species at a time in series, that doesn’t prove Darwin’s followers are wrong about human origins, but the situation gives no particular support to their theory as opposed to others.