Homo Heidelbergensis is now being relegated as a side branch to the human line?? The nuclear DNA from the Sima de los Huesos Heidelbergensis (recently, like 2021), and it’s proto Neanderthal, pushing the common ancestor to humans back to 800kya?? Help me here… Am I understanding this right?? Though we may have interbred with the Heidelbergensis/Neanderthal subspecies, they don’t account as our direct ancestors. This means we are left with a massive gap between homo erectus and modern humans, with little to nothing to show by way of remains?
I’m not a paleoanthro guy by any means, but it looks to me like:
(1) they’re simply saying that Heidelbergensis has been a bit of a wastebasket taxon and needs to be broken up, with some of the pieces being plausible ancestors of the branch leading to modern humans and some not. This type of criticism isn’t uncommon in paleoanthropology, and the lumpers are now taking their lumps from the splitters. I think that Ian Tattersall has described erectus and habilis as wastebasket taxa, too, and he suggests that some of the excessive “lumping” is due to a bias in favor of there being a single clear line through early humans leading to moderns rather than a more typical “bushy” phylogeny. He blames Ernst Mayr, among others, for that.
(2) In paleontology generally I don’t think there are a lot of people who like to definitively identify anything as an ancestor of any modern species. The main reason for that is that you just can’t actually tell. Something could be a direct ancestor, or it could be a very close cousin. Analysis of characteristics can tell you that something doesn’t look like you’d expect a direct ancestor to look like (e.g., it has “derived” characters of its own that aren’t in the modern species), or that it looks consistent with being a direct ancestor, but nothing can tell you that it IS a direct ancestor unless you find a line of 'em with their family bibles buried next to 'em with all the relationships written down. That doesn’t happen a lot.
So instead of that “massive gap” I think it’s more like we have a confusing bush. We spent too much time stuffing bones into a nice trim line of descent and supposing that H. erectus was a good taxon and that it was ancestral to H. sapiens. But what if erectus isn’t really a species, but a tag we stuck on a diverse assemblage of critters? What if species are sort of hard to resolve over such short time scales? We in the general public who are accustomed to asking simple questions like “is this guy my ancestor or not” are going to have to get used to the questions being more complicated and the answers being more confusing.
I am pretty much on board with Puck. But the bush of lineages to me is more like a bush of subspecies rather than species. Neanderthals interbred with H. sapiens, so one species. Then there are the Denisovans interbreeding with both of those, so one species. Then comes the discovery from the Republic of Georgia of a bunch of skulls from beings that lived in the same area and in a similar time frame. But anatomical comparisons puts some skulls with H. erectus, another with the smaller brained H. habilus, and another with H. heidelbergiensis. So all of those are arguably … one super variable species which we can call H. erectus because that name takes precedent. It’s when we get small samples that we can get fossils that say this one is discreetly in this taxon, and that one is in that taxon over there. If we had lots more fossils, we might find they are pretty much in a continuum.
Right. So homo sapiens sapiens come out of Africa 150k-200k with a pretty similar genome to modern humans. Then they have minimal inbreeding with Neanderthals (who came from Heidelbergensis) and pick up some useful genes (and no mitochondrial or Y-chromosomal DNA). But, those archaic hominis were our common ancestors from a side branch 800kya. So where are the fossils of any hominins from 800kya-200kya that directly led to humans? There is a pretty massive gap between Erectus and H. Sapiens Sapiens, and if we can’t count H. Heidelbergensis as one of those we don’t have any fossils of direct ancestors. We find fossils of H. Erectus, which are much older than this missing lineage between 800kya-200kya.
But this paper doesn’t even propose that none of the specimens identified as H. heidelbergensis could be ancestral to modern humans. It merely suggests that the taxon should be broken up – that it has been, as is sometimes said (though I don’t think these authors used the expression), a “wastebasket” taxon.
It’s probably best not to fixate on species labels too much, when questions of assignment of individuals to those labels are as much in flux as they can be in human ancestry. You don’t fill a “gap” in sequence with a label; you fill it with the actual specimens, when possible, and in accord with modern phylogenetic practice what you’re going to wind up with are a bunch of terminals on a cladogram, without attribution of direct ancestry. That doesn’t mean none of those terminal taxa are ancestral. And the nice straightforward structure of a cladogram falls a bit short of resolving the complexity of nature when you have multiple populations that may be hybridizing.
But bear in mind that it might well be that we don’t have a lot of remains of direct ancestors in certain periods. Limited range, ecological issues, basic problems of taphonomy – all that comes into the mix. What if some important speciation event is happening in some peripheral isolated population? What are your chances of fossils from that particular isolate? What if this is going on in an environment not conducive to fossilization? If your ancestors are all getting eaten by scavengers and then getting composted on the forest floor, there aren’t going to be a lot of remains to study. And how plentiful are these ancestors of ours?
In other words: we can’t stand here in the present and demand that the fossils speak. We’d like to. Everyone would like to. But, you know, while it is untrue that it’s impossible to tell the sun not to shine, it is unreasonable to expect compliance. The same is true for the fossil record. We all want more fossils. But there is no tribunal to which we can bring our complaint, if that complaint is that we don’t have enough of them.
The article unfortunately doesn’t cite its source in the literature. Do you know what it was? Do you know how they determined what specimens belong to what species? Did they declare a type specimen? How do they know this is a species, and how do they know it’s ancestral?