I was listening to one of my favourite podcasts the other day (The Skeptics Guide to the Universe, check it out, it’s awesome) as they discussed some new papers about hominin skulls.
The first was a paper from China, published in Science, in which two crania are described that have both modern human and neanderthal features. They had a large, lightly-built brain case with a soft brow, like we do; but they also had “occipital (suprainiac and nuchal torus) and temporal labyrinthine morphology” which, according to Google, is an unusual way for the back of a skull to join up peculiar to neanderthals.
We have known for a few years now that the genome of any European contains about 1-4% neanderthal DNA, meaning that we didn’t just outcompete them but we also, well, knew them in a biblical sense. What we hadn’t seen before, though, was an actual specimen displaying the mix of features you might expect. Whilst we only have a few percent neanderthal in us now, there must be lineages from 50,000 years ago that had a much higher proportion.
The second paper was from a Portuguese group and published in PNAS (open access). In it they describe a skull they discovered in the Gruta da Aroeira cave in Portugal dating to about 400 thousand years ago. Once again, this skull shows some features of two different human species, neanderthals and homo erectus.
Each of these skulls are interesting in their own right but the latter authors used this opportunity to make a point that I, certainly, had never thought of and was something of an epiphany for me. In their paper they opt not to assign the skull a taxonomic name even though they could. They did this because the authors believe that the idea of there being several distinct human species throughout Eurasia over the past half million years is misleading and, indeed, wrong.
They are of the opinion that there was a continuum across the continent, all of one human species, and that what we are seeing today is an effect of sampling just a very few examples of this one sprawling, varied species. This would mean that the neanderthals, homo erectus, homo heidelbergensis, the Denisovans, homo naledi, homo floresiensis and the others of the homo genus that escape me right now are all one and the same species, in effect, they don’t exist separately and are just an artefact of the fossil record, at best a group of subspecies.
I suppose this shouldn’t come as too much of a shock. All domestic dogs are wolves, we know that. They are all Canis lupus and quite capable of breeding with a wolf – assuming they survive the process – and, after all, two individuals being able to breed is the go to definition of what a species is.
As we gather more genomic data on the Homo genus we are realising that the individual species are not distinct, there is definitely overlap. If all these groups were capable of interbreeding, then, it really wouldn’t be accurate to list them as separate species.
The epiphany for me came when I realised that this meant I literally am a neanderthal. I am a H. erectus, and so are you, we all are. There is no meaningful taxonomic difference between you and them. That, to me, is amazing and makes the ridiculous segregation of people by the colour of their skin that we have seen, and continue to see, in human societies even more absurd than it already was.
I will caveat this by saying that not all paleoanthropologists agree with this theory; this is not yet the received wisdom and, maybe, it never will be, but I’m going to run with it. We are all human. You could probably breed with a Denisovan or a neanderthal, again, assuming you survive the process.