Far from there being no transitional fossils as Creationists claim, we now have what's turning out to be too many of them. Rather than the tree of human evolution being a simple one with just a single branch off the African ape limb, it's turning out to be a much richer, more complicated and interesting one with several different hominins co-existing for most of our history. In fact, the last few thousand years, since the last Neanderthals and Denisovans died out as distinct species, have been unusual and maybe unprecedented; we are now the only member of the Homo genus to survive.
As an article in New Scientist says:
[I]t looks if as many species of human-like apes were around during the crucial period from 2.5 to 1.8 million years ago, when the first upright apes with relatively large brains evolved. What's more, the East African hominin long seen as our direct ancestor may be just a cousin, with our true roots lying further south. Our family tree may have to be completely redrawn.
At one time the human evolutionary story looked fairly straightforward and linear, rather like the March of Progress which was drawn for a popular science book in 1965. It looked like Homo habilis from Tanzania was the 'missing link' between the earlier African Australopiths and H. erectus, fossils of which had been found in Africa and Asia and which was therefore assumed to be our direct ancestor. H. habilis was designated Homo because it was assumed to be the first of the genus.
Then the picture became a little more confused by the discovery of what was thought at first to be an australopith living at the same time and in the same area as H. habilis but is now called Paranthropus boisei which had a large brain but which had some distinctly un-human characteristics. For this reason it was given a side-branch of the main Homo tree.
Then researchers in Tanzania began to find skulls and other remains which had a slightly larger brain than H. habilis and a broader face but which were also contemporary with H. habilis and P. boisei. These have been tentatively named H. rudolfensis but is more usually referred to by the number of the original skull find, KNM-ER 1470 or 1470 for short.
And now it gets even more complicated. Fossil fragments of what look suspiciously like H. erectus, from the same time and place as the other three species have also been found. If these are indeed from H. erectus it probably solves the problem of where H. erectus originated - Africa or Asia - but it also adds another complication. Obviously, if H. erectus and H. habilis co-existed it's unlikely (not impossible) that H. habilis was ancestral to H. erectus.
As though that wasn't enough some researchers have even proposed a fifth species from the same period albeit based on a single jawbone and not universally accepted as distinct from 1470. The probability remains however that there were at least four and maybe five different hominin species co-existing in close proximity in East Africa.
So, rather than no transitional fossils, we have too many if anything.
And now we have yet another complication. Cue Australopithicus sediba, from way south of the East African group, in South Africa near Johannesburg. I've blogged before about this newly discovered species, from two very well preserved fossil specimens; one of an adult female and the other a juvenile male. It comes as close as anything to being a transitional species from the time when humans were moving down from trees, adopting a bipedal gait and taking to the ground, so diversifying from the chimpanzee branch which remained arboreal. This might well have been driven by climate change as southern Africa was changing from forest to savannah.
A. sediba had a pelvis and lower limbs of a hominin and the skull and upper limbs of a chimpanzee apart from the teeth and hands which look distinctly human. There are also signs of an enlarging brain. In an amusing piece of research by the Boston Museum of Science, MA, USA recently, it was found that one in thirteen of 398 visitors to the museum had feet like A. sediba.
Colin Barrass again:
Wood, at least, is confident of the way the wind is blowing. He predicts that by 2064 – a century after the first H. habilis finds were described, and 99 years on from The March of Progress – our family tree will be even bushier and more tangled than he currently envisions it. If the discoveries keep coming thick and fast, we might not have to wait that long to find out whether or not he is right.
Another transitional species'; another 'missing link' and rather than clarifying the picture it shows us that our evolutionary history in Africa was far from simple and we now have three competing models for our evolution. We seem to be the lucky ones who didn't go extinct and for most of our history we lived alongside other close relatives.
Of course, those of us that came out of Africa also experience living alongside the descendants of an earlier form until just a few thousand years ago. What would a Creationist today make of there being two or three other human species around? Which of them would be the favourite of their imaginary daddy in the sky and how quickly would they kill the ones which 'Satan' had obviously created?
Unlike Creationists who crave simplicity and demand a very clear picture which a five year-old could understand, regardless of whether it's right or wrong, science is very comfortable with lack of clarity for the time being, confident that eventually, if and when all the pieces are in place, the right picture will emerge. Science enjoys the challenge of conflicting and confusing evidence, of disagreement and the search for those vital scraps of evidence because that is the only way - the only honest way - to get ever closer to the truth. No half-decent scientist would be willing to settle for easy answers because they conform to a preconceived, evidence-free superstition learned at his or her mother's knee.
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