Creationists now have another problem and it's not just 250,000-year-old fossils in a 10,000-year-old Universe. It's even more fundamental than that.
First, a little background:
Homo naledi is from South Africa and, like another South African hominid, Australopithecus sediba, has a mixture of very human physical characteristics and some very primitive ones. With A. sediba, the primitive characteristics are enough to place it in the Australopithecus genus and so either an ancestor of the Homo genus or a cousin of one of our ancestors.
Embarrassingly for creationists, A. sediba is almost exactly what you would expect a species intermediate between an arboreal ape and a terrestrial Australopithecine to look like. It has brachiating arms and upper body on a bipedal lower body, with a very human-looking foot.
This is astonishingly young for a species that still displays primitive characteristics found in fossils about 2 million years old, such as the small brain size, curved fingers, and form of the shoulder, trunk and hip joint... It could lie close to the origin of the genus Homo, suggesting that this is a relic species, retaining many primitive traits from a much earlier time.
H. naledi also has a mixture of primitive and modern features, in this case, a head with a brain-case little larger than a chimpanzee on a distinctly human body. To all intents and purposes, H. naledi was a species of human with an ape brain. Just what you would expect of a transitional species midway between an Australopithecine and a hominin, in fact. If you could ever tie a creationist down to a description of what they would expect a transitional species to look like, they would be hard-pressed not to come up with something very much like H. naledi.The question was always where, as with A. sediba, H. naledi fitted in the hominid family tree. This was made especially complicated by the generally accepted idea that the earliest hominins - something like H. habilis - evolved from a late Australopithecine - something close to A. afarensis - in East Africa, probably Ethiopia. So, what is an early hominin doing in South Africa?
Now this question has been further complicated by yesterday's news that H. naledi was not as old as previously believed but was around between 200,000 and 300,000 years ago - at a time when H. sapiens was around! It is distinctly possible that the two species, H. naledi with a human body and small-brained ape head, and H. sapiens were around at the same time and maybe even in the same area. In fact, it now becomes a possibility that early modern humans were responsible for H. naledi's extinction.
There are obvious parallels with the late survival of H. floresiensis in Indonesia, but in that case island isolation probably accounts for its longevity. How did a comparably strange and small-brained species linger on in southern Africa, seemingly alongside more ‘advanced’ humans?
This is not the first time that two or more hominins have been shown to co-exist, sometimes even in East Africa, and of course we have the example of H. sapiens, H. neanderthalensis and almost certainly the yet to be officially named Denisovans, all being contemporary in Eurasia and even interbreeding. What is unusual in the H. naledi case is that the two contemporary species look so widely spaced evolutionarily. How did a primitive, and one assumes not very technologically advanced or intelligent hominin, co-exist with the highly intelligent early modern humans?There is a similar example in H. floresiensis, the 'Hobbit', which survived on Flores Island in Indonesia even though, as was shown only last week to be close to a very early hominin, possibly H. habilis or an immediate ancestor, until about 50,000 years ago. But surviving on a relatively isolated island is a lot easier to explain than surviving in South Africa alongside modern humans.
There is also the question of how H. naledi survived alongside more advanced members of the Homo genus. If environmental pressures were driving their evolution why weren't the same pressures driving H. naledi to evolve more advanced features such as a larger brain?
So, what are the possibilities?
- H. naledi survived because modern humans had not in fact spread into its range earlier, so it had no competition.
- The environment in South Africa up to 250,000 years ago did not require advanced intelligence to survive, whereas East Africa and especially the Ethiopian highlands was much more demanding.
- Hybridisation. Just as H. sapiens in now known to have interbred with other contemporaneous hominids at least in Eurasia, it is possible that they could have interbred with Australopithecines in South Africa.
All the remains of H. naledi so far recovered have been from a single chamber deep the Rising Star Cave system in Gauteng province. It appears that the bodies were placed there, and this would probably have required some form of torch to see the way. This suggests a mastery of fire, a sense of purpose, a level of social organisation and maybe a respect for the dead which may indicate some sort of ritual burial. Did a hominid with an ape brain have this degree of social organisation, even religion? We are of course assuming here that the remains were placed in this chamber by other members of the same species. This might not necessarily be true!
There are still some intriguing questions for science raised by H. naledi and particularly by its apparent long survival; none of these are insurmountable or bring into question the general idea of human evolution in Africa. All we are talking about here is the fine detail. But for creationists the questions appear to be at least as difficult as those raised by H. floresensis:
Why is H. naledi not an intermediate species coming somewhere between an Australopithecine and a hominin? Is it an ape with a human body below the neck, or a human with an ape's head? Why, if evolution cannot produce a new species, let alone a new genus, does this species appear to combine the features of two different genera, hominins and australopithecines?
How does the existence of this species and the unmistakable evidence that modern humans emerged by an evolutionary process from non-human ancestors, fit in with the notion of original sin committed by a single ancestral couple?
And lastly, why is it so much older than they believe the Universe to be?
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