At least according to a paper in Arizona, which proclaims that “Research by UA assistant anthropology professor David Raichlen and his colleagues provide evidence suggesting that 3.6 billion years ago, hominins walked with the same upright gait that humans do today...”
Link: Arizona Daily Wildcat
Really, upright hominins 3.6 BILLION years ago??? Bipedal locomotion is one thing, but upright walking during the Archean that’s impressive - especially considering the lack of oxygen.
Incidentally, the mentioned research actually makes an argument for hominin bipedalism first occurring around 3.6 MILLION years ago. And the research is not a challenge to evolution; in fact, it fully endorses it.
The research is available at PloS; here’s the abstract:
Debates over the evolution of hominin bipedalism, a defining human characteristic, revolve around whether early bipeds walked more like humans, with energetically efficient extended hind limbs, or more like apes with flexed hind limbs. The 3.6 million year old hominin footprints at Laetoli, Tanzania represent the earliest direct evidence of hominin bipedalism. Determining the kinematics of Laetoli hominins will allow us to understand whether selection acted to decrease energy costs of bipedalism by 3.6 Ma.
Using an experimental design, we show that the Laetoli hominins walked with weight transfer most similar to the economical extended limb bipedalism of humans. Humans walked through a sand trackway using both extended limb bipedalism, and more flexed limb bipedalism. Footprint morphology from extended limb trials matches weight distribution patterns found in the Laetoli footprints.
These results provide us with the earliest direct evidence of kinematically human-like bipedalism currently known, and show that extended limb bipedalism evolved long before the appearance of the genus Homo. Since extended-limb bipedalism is more energetically economical than ape-like bipedalism, energy expenditure was likely an important selection pressure on hominin bipeds by 3.6 Ma.
Raichlen, D., Gordon, A., Harcourt-Smith, W., Foster, A., & Haas, W. (2010). Laetoli Footprints Preserve Earliest Direct Evidence of Human-Like Bipedal Biomechanics PLoS ONE, 5 (3) DOI: 10.1371/journal.pone.0009769