Wednesday, 17 July 2013

Too Many Transitional Fossils

Australopithecus sediba
The strange ape that's rewriting our family tree - life - 15 July 2013 - New Scientist

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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7 comments :

  1. The biggest problem for creationists though is that they cannot even agree on the out of Africa hypothesis.

    ReplyDelete
  2. What an excellent and informative article Rosa. The real science is always so much more interesting than any creationist propaganda. I particularly like your final paragraph as it perfectly sums up my own feelings and experiences in dealing with creationists. It's like they require a 100% accuracy frame-by-frame video recording of the entire evolutional process from start to present day, to be convinced of anything (a standard of proof which would never be required, for instance, in a court of law), yet have absolutely no credible theories of their own. They just can't accept that the science is still finding more answers, and we don't have the complete picture yet. But that's science - we will likely never know absolutely everything there is to know about evolution.

    ReplyDelete
  3. So demonstrate they are different species. Remember, the domestic dog varies widely in appearance but they are all one species.

    I must confess that I find it rather funny that world of Evolutionism imagines that the size of the brain is an indicator of intelligence when it has been known for some time that it isn't. Still you do like your fairy stories.

    Remember, science is about observing and testing an event repeatedly. Not about taking random samples, deciding on what event you want to prove and putting them in an order that seems to prove your claim.

    ReplyDelete
    Replies
    1. Of course they are different species - who suggested otherwise?

      Evolution explains how one species slowly changes over time into one sufficiently different for taxonomists to classify it as a different species to its ancestor.

      I'm astonished that you were unaware of this. Given your eagerness to dismiss the evidence for evolution one might have expected you to learn something about the subject first, though I can understand your reluctance to.

      The question is, how you know what facts you must avoid learning just in case they shake your unshakable faith.

      Delete
    2. There is no evidence for Evolution, if there were you would be able to demonstrate the descent of all life from an original form.

      And no, there is only one species of Man and he hasn't descended from any sort of ape - or any other creature. Differences of appearance cannot be used to distinguish species, whatever the taxonomist may tell you. That is why they are reducing the number of dinosaur species.

      Seems it is you who has the unshakeable faith, not me. Or at least my faith is in one whom I know and trust, yours is in the claims of your fellow believers.

      Delete
    3. When do you plan to publish this astounding finding in a peer-reviewed biology journal? I'm sure biologists would be interested to discover that they are all wrong.

      Hint: refusing to look at the evidence doesn't make it go away. I hope that helps.

      Delete
    4. Martin.

      Unless you have something interesting and original to say, could you find somewhere else to post your hopeful assertions, please. Typing things out here doesn't make them come true.

      Delete

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