We've never walked alone- whether chimpanzee or hominin !

By Dave Armstrong - 02 Aug 2016 23:0:0 GMT
We've never walked alone- whether chimpanzee or hominin !

Laetoli hominin and chimpanzee footprints. These randomly selected footprints demonstrate the 'stereotypical' morphologies of, from left to right, human, Laetoli hominin and chimpanzee footprints. The human and chimpanzee prints were produced experimentally in this study. The Laetoli footprint shown here is G1-25. The top row includes standard photographs of these footprints while the bottom row shows depth-coloured maps of the same tracks pictured above, to emphasize their three-dimensional topographies. In the depth-coloured maps, dark blue corresponds to areas of greatest depth and depths become shallower along the gradient from blue to green to yellow to orange. Important morphological comparisons described in the main text include the similarity of proportional toe depths (toe relative to heel depths) of the Laetoli and chimpanzee footprints and their distinction from proportional toe depths of modern human footprints, and the intermediate depth of the medial midfoot region in the Laetoli tracks. Images are not set to common scale. Footprint images; Credit: © rspb.royalsocietypublishing.org

41 barefoot humans, 2 chimpanzees and some fossil tracks that seem to be Pliocene (specifically 3.66million years old)Australopithecus afarensis have been extensively compared. The ancient footprints indicate a large limb flexing when the foot touches the ground and a flat-footed landing. Both chimpanzee and human are very different in their walking, although the toes of both, humans particularly, make very obvious impressions in their tracks. The little hominin from Tanzania is also quite distinct, shaped in a human way, but with differing pressures exerted.

The fact that we are 2-legged is critical to our development, our cultures and to how we cope with modern life since before the Stone Age. Bipedalism determines how we have made war, clothes, prepared food, and, most obviously, hunted. It has made our hand available as a tool and tool-maker and released the arms for throwing, holding and many other functions. Our frequent bad back-aches, are partly due to the genetic remainder of our quadrupedal ancestry, while those knees are barely suitable for purpose!

This gives great interest to the research that attempts to discover how our hominin bipedalism evolved into hominid walking, running and jumping. When the Pliocene saw the hominin tracks at Laetoli in Tanzania, this was the first known evidence of our ancestors 2-legged habit - in this case, probably walking. This means that whether they were Australopithecus or not is irrelevant. Hadar in Ethiopia has such fossil bones, but too many arguments rage over what the leg bones can indicate about gait.

The analysis took account of the big toe of the ancient hominins, which is orientated differently from ours. There was also a relatively deep impression made by the heel and midfoot, especially when compared to the toes, which made practically no impression compared to the gripping human phalanges. The famous fossil of Lucy has often been said to have a pelvic shape that means the gluteal muscles could not have maintained any human-like balance or stability when walking. It is therefore no surprise that the authors of this paper also suggest a bent hip and bent knee approach to walking, just as the chimpanzee does, but to a much lesser extent. If you look at the footprint however, the obvious difference is the massive use of the chimpanzee hallux (big toe.)

Studying modern humans, we are aware that we are supremely modified to save energy when running or walking. This achievement was beyond or possible ancestor, as it is for the other apes. Home-range size for hominins would be more restricted than modern humans, and not just because of their small size. Tree climbing may well have been a more productive occupation than long-distance foraging.

This very interesting paper is produced today in the Proceedings of the Royal Society B, written by Kevin G. Hatala, Brigitte Demes and Brian G. Richmond of the Max Planck Institute for Evolutionary Anthropology, Leipzig and the George Washington University DC and Stony Brook University, NY, both in the US.