Saturday, 1 June 2013

Walking Out Of Africa

A. sediba compared to a modern human (L) and a chimp (R)
The devastation for Creationism continues as more and more evidence piles up confirming the universally-held view of serious biologists, anatomists and paleoanthropologists, that Darwinian Evolution is the only theory which accurately explains the observable fact of evolution in general and human evolution in particular. The observable fact is of course the fossil record which shows evidence of gradual change over time, which is becoming more and more complete, and which has never once produced an authenticated specimen which doesn't fit. The pieces of the puzzle are all falling neatly into place.

Last April, BBC News Science and Environment carried an interesting article about the most complete reconstruction yet of a possible human ancestor from South Africa. To the embarrassment of Creationists it showed a remarkable mixture of human and chimpanzee characteristics.

While the upper body and skull more closely resembled that of a chimpanzee, apart from the hands and teeth, which look human; the pelvis and lower limbs look like those of modern humans, until, that is, you look at the feet. They have several chimpanzee-like features. If that doesn't meet Creationist loons' incessant demands for an ape-human transitional fossil, nothing will - and I suspect nothing will, at least for Creation pseudo-scientists, because that would mean abandoning a lucrative source of income.

The reconstruction was done using remains of two individual skeletons of Australopithicus sediba found together in a depression at Malapa, north of Johannesberg. One is of an adult female; the other of an adolescent male. It is thought they could be mother and son who met with a fatal accident together.

As the article said:

An analysis of Au. sediba's lower limb anatomy by Jeremy DeSilva from Boston University and colleagues suggests that the species walked in a unique way.

Its small heel resembles that of a chimpanzee more than it does a human. This suggests it likely walked with an inward rotation of the knee and hip, with its feet slightly twisted.

This primitive way of walking might have been a compromise between upright walking and tree climbing, the researchers suggest, since Au. sediba seems to have had more adaptations for tree-climbing than other australopithecines.

The findings suggest that some species of australopithecine climbed trees, some walked on the ground, and some did both.


The research has implications for how we interpret the fossil record and the evolution of these features.
It's good to understand the normal variation among humans before we go figure out what it means in the fossil record.

Tracy Kivell, Palaeoanthropologist,
Max Planck Institute for Evolutionary Anthropology
From this we get a picture of the australopithecines radiating as they moved from an arboreal existence to living on the African plains. This is reinforced by the findings of Joel Irish from Liverpool John Moores University and colleagues who found that Au. sediba's teeth resembled those of Au. africanus, also from southern Africa, suggesting at least two main groups of australopithicines; one in southern Africa and another further north in Ethiopia, including Au. afarensis ("Lucy").

And now today comes more devastating news for Creationists to ignore. BBC News Science & Environment today carries an article by Science Reporter, Melissa Hogenboom (Ape-like feet 'found in study of museum visitors'). Apparently, Au. sediba wasn't the only hominin with those chimpanzee-like foot features. Of 398 modern human visitors to the Boston Museum of Science, MA, USA, one in thirteen had differences in foot-bone structure similar to those of Au. sediba. This finding has been published in Science Journal.

Jeremy DeSilva from Boston University and a colleague asked the museum visitors to walk barefoot and observed how they walked by using a mechanised carpet that was able to analyse several components of the foot.

Floppy foot

Most of us have very rigid feet, helpful for stability, with stiff ligaments holding the bones in the foot together. When primates lift their heels off the ground, however, they have a floppy foot with nothing holding their bones together. This is known as a midtarsal break and is similar to what the Boston team identified in some of their participants. This makes the middle part of the foot bend more easily as the subject pushes off to propel themselves on to their next step.

Dr DeSilva told BBC News how we might be able to observe whether we have this flexibility: "The best way to see this is if you're walking on the beach and leaving footprints, the middle portion of your footprint would have a big ridge that might show your foot is actually folding in that area."


So it looks for all the world as though our feet are still evolving and that many of us carry this fossil record of our anatomical history. Don't be at all embarrassed if you have these feet, like about 8% of people who visit museums in Boston, MA. Wear them like a badge of honor. Those feet have walked a long way from Africa over the last two million years. I don't have those feet but I'm proud to wear a badge of an even longer evolutionary journey. I have primitive ears, and no one can take that away from me.

References:
  1. Team reconstructs 'human ancestor' - BBC News Science & Environment
  2. Ape-like feet 'found in study of museum visitors'; Melissa Hogenboom, Science reporter, BBC News
  3. DeSilva, J. M. and Gill, S. V. (2013), Brief communication: A midtarsal (midfoot) break in the human foot. Am. J. Phys. Anthropol.. doi: 10.1002/ajpa.22287





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1 comment :

  1. This is interesting, however we should be careful as there are experts who are still debating whether these new Australopithecus sediba fossils actually fit into the evolutionary tree were we think they do.
    The link is subscription access, but just in case you have it.http://www.nature.com/nature/journal/v497/n7451/full/497573a.html

    However this does not detract from the fact that evolution is still happening.

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