UK researchers have contributed a fascinating study of assisted bipedalism in orangutans. These animals can keep their legs straight as they move through trees with support provided by the arms. This mode of locomotion occurs when the animals are feeding from small, flexible branches or moving between trees. "Our results are consistent with the prediction that bipedalism allows orangutans to move along multiple supports that are more slender, and hence more deformable, than does quadrupedalism or even orthograde suspension." This confirms the hypothesis that hand-assisted bipedalism confers selective advantages on arboreal apes.
However, the empirical research is not the reason why this paper was the cover story in Science. The authors use their study to argue that bipedalism is a trait that evolved in an arboreal context. One media story describes the significance thus: "The new theory marks a U-turn in scientific thinking. Previously it was assumed humans only began to stand upright after moving out of the forests on to the wide open savannahs of East Africa." The authors claim: "Hand-assisted locomotor bipedality, adopted under these strong selective pressures, seems the most likely evolutionary precursor of straight-limbed human walking."
Although the paper has created a stir, what has been totally lacking is a design perspective. This, I think, is to the detriment of the scientific debate. In particular, the differences between "hand-assisted locomotor bipedality" and the bipedality evidenced by humans are not explored. Yet a fundamental aspect of design thinking is that a whole raft of characters must be in place to enable humans to balance and move on two feet! These include: arched feet, strong big toes, long legs, upright knee joints, angled femur bones, upright hip joints, straight back, upright skull, flat face and a very fine sense of balance. To develop a coherent account of the origin of bipedalism from a "hypothetical common ancestor of the great apes", observations of orangutans moving through trees with straight legs must be supplemented by an extensive analysis of other relevant information. In this analysis, design perspectives have a significant contribution to make.
Another conclusion of interest is that knuckle-walking is inferred to be a derived (rather than a primitive) feature. They suggest that early bipedalism was retained, not gained, in humans but lost by apes and chimps. One is tempted to observe that many widely-held scenarios about human evolution have had to be abandoned like this. Adopting a cautionary stance does seem the wisest long-term strategy.
One last point: the debate over bipedality has artificially restricted boundaries. The participants are all presuming that there is a "hypothetical common ancestor of the great apes". There is no hypothesis that there may not be such an ancestor. This is because the evolutionary framework is accepted as a 'given', deemed to have been proved long ago and not worth revisiting. Consequently, this whole exercise is an example of Kuhnian 'normal' science. The researchers are working within a closed paradigm and trying to put the jigsaw together. Some of us want to change the boundaries of the debate, to revisit the claims of evolutionary theory and to test hypotheses that others are not testing. This, we think, should be deemed essential for the health of science.
Origin of Human Bipedalism As an Adaptation for Locomotion on Flexible Branches
S. K. S. Thorpe, R. L. Holder, and R. H. Crompton
Science, 316, 1 June 2007: 1328-1331.
Abstract: Human bipedalism is commonly thought to have evolved from a quadrupedal terrestrial precursor, yet some recent paleontological evidence suggests that adaptations for bipedalism arose in an arboreal context. However, the adaptive benefit of arboreal bipedalism has been unknown. Here we show that it allows the most arboreal great ape, the orangutan, to access supports too flexible to be negotiated otherwise. Orangutans react to branch flexibility like humans running on springy tracks, by increasing knee and hip extension, whereas all other primates do the reverse. Human bipedalism is thus less an innovation than an exploitation of a locomotor behavior retained from the common great ape ancestor.
O'Higgins, P. and Elton, S., Walking on Trees, Science, 316, 1 June 2007: 1292-1294.
Gibbons, A., Walk Like an Orangutan, ScienceNOW Daily News, 31 May 2007.
Breitbart.com, May 31 2007, Humans 'learned to walk in trees'
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Evolution has become a favorite topic of the news media recently, but for some reason, they never seem to get the story straight. The staff at Discovery Institute's Center for Science and Culture started this Blog to set the record straight and make sure you knew "the rest of the story".
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