Saturday, December 16, 2017

Walking 2 Million Years Ago: More Efficient Than Today?

Do you walk like a caveman?

In an article published recently in the American Journal of Physical Anthropology, researchers from the Paleophysiology and Ecology Group of the Centro Nacional de Investigación sobre la Evolución Humana (CENIEH) analyzed the influence of body proportions on the cost of locomotion by means of an experimental energetic study with 46 subjects of both sexes, whose results indicate that the walk of Pleistocene hominins was no less efficient energetically than that of current humans.

The energy cost of locomotion is a question that has been widely studied and debated within Paleoanthropology because of its important implications. The researchers used the relationship between the width of the hip, the length of the femur and the body mass to model this cost in a large number of extinct hominins.

Energetic cost of walking
Credit: Centro Nacional de Investigación sobre la Evolución Humana (CENIEH

Traditionally, it was thought that the leaner skeletons of modern humans reflected biomechanical advantages which made locomotion a more efficient activity. The slimmer pelvis of our species entails greater difficulty for childbirth, but it reduces the force the abductor muscles of the hip have to exert to maintain the stability of the pelvis while walking.

Nevertheless, as Marco Vidal Cordasco, lead author of this article, entitled Energetic cost of walking in fossil hominins, explains: “That doesn’t imply that the hominins with wider pelvises expend more energy walking. In fact, the results obtained show that wider pelvises, at the height of the iliac crest, allow the energy cost of locomotion to be significantly lower”.

Upward metabolic readjustment

Since two million years ago, with the appearance of the species Homo ergaster, the body mass and the brain size of the hominins have risen considerably. These changes have entailed an important readjustment at the metabolic level, with greater demand for energy to maintain these larger organs.

Homo ergaster reproduction
Credit: Nachosan , Wikimedia Commons

“However, our results show that the greater efficiency of locomotion was not a mechanism to compensate for this increase in size. That is to say, the changes observed in the width of the pelvis and the length of the lower limbs did not reduce the cost of walking sufficiently to offset the rise in energy cost caused by the increased body mass”, adds Vidal.

Homo ergaster (meaning "working man") or African Homo erectus is an extinct membrer of the genus Homo that lived in eastern and southern Africa during the early Pleistocene, that is, between 1.9 million and 1.4 million years ago. It is one of the earliest hominins, which are those hominids that  comprise the original members and species of the human clade after splitting from the line of the chimpanzees.

Hominin Footprints from Early Pleistocene Deposits at Happisburgh, UK Figure 1. Map of Pleistocene footprint sites dating from prior to 40 ky in Africa and Eurasia.
Credit:  Nick Ashton Simon G. Lewis Isabelle De Groote Sarah M. Duffy Martin Bates Richard Bates Peter Hoare Mark Lewis Simon A. Parfitt Sylvia Peglar Craig Williams Chris Stringer

Investigations at Happisburgh, UK, have revealed the oldest known hominin footprint surface outside Africa at between ca. 1 million and 0.78 million years ago. The site has long been recognised for the preservation of sediments containing Early Pleistocene fauna and flora, but since 2005 has also yielded humanly made flint artefacts, extending the record of human occupation of northern Europe by at least 350,000 years.

Hominin Footprints from Early Pleistocene Deposits at Happisburgh, UK.
File:Happisburgh Footprints 01.jpg
Credit Martin Bates / PLoS One /Wikimedia Commons

Using foot length to stature ratios, the hominins are estimated to have been between ca. 0.93 and 1.73 m in height, suggestive of a group of mixed ages. The orientation of the prints indicates movement in a southerly direction on mud-flats along the river edge. Early Pleistocene human fossils are extremely rare in Europe, with no evidence from the UK. The only known species in western Europe of a similar age is Homo antecessor, whose fossil remains have been found at Atapuerca, Spain. The foot sizes and estimated stature of the hominins from Happisburgh fall within the range derived from the fossil evidence of Homo antecessor.

Contacts and sources:
Centro Nacional de Investigación sobre la Evolución Humana (CENIEH

Citation: Vidal‐Cordasco, M., Mateos, A., Zorrilla‐Revilla, G., Prado‐Nóvoa, O., Rodríguez, J. (2017). Energetic cost of walking in fossil hominins. American Journal of Physical Anthropology, 164(3), 609-622.

Citation: Ashton N, Lewis SG, De Groote I, Duffy SM, Bates M, Bates R, et al. (2014) Hominin Footprints from Early Pleistocene Deposits at Happisburgh, UK. PLoS ONE 9(2): e88329.

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