Ancient hominins were walking in a decidedly “human-like” manner some three million years before Homo sapiens evolved, researchers have discovered.
By analysing 3.6 million-year-old fossilised footprints discovered at Laetoli in Tanzania, then comparing the findings with footprints made by human volunteers walking in different postures, David Raichlen from the University of Arizona, US, concludes that true bipedalism, with the legs fully extended, arose in the hominin line much earlier than previously thought.
“Fossil footprints are truly the only direct evidence of walking in the past,” says Raichlen.
“By 3.6 million years ago, our data suggest that if you can account for differences in size, hominins were walking in a way that is very similar to living humans. While there may have been some nuanced differences, in general, these hominins probably looked like us when they walked.”
Prior research on fossil hominin foot bones suggests that walking on two legs emerged earlier than 3.6 million years ago, but was part of a crouched and shuffling gait. True bipedalism, some scientists suggest, did not begin until around 1.8 million years ago, with Homo ergaster.
Raichen’s findings, however, suggest otherwise. His latest work – presented as an abstract to the annual Experimental Biology Meeting held in April in San Diego, California and sponsored by the American Association of Anatomists – comes on the back of much previous research investigating the biomechanical differences between human and other ape methods of walking.
After taking careful morphological measurements of the Tanzanian footprints, he enlisted the help of a group of human volunteers. He asked his helpers to walk, adopting different postures – fully upright, and crouched – then analysed the resulting footprints.
He discovered that the prints produced by the upright walkers were a much closer match to those of the ancient hominin who walked at Laetoli. The finding was broadly in line with his previous work, which established that fully upright bipedal walking requires 75% less energy than the sort of crouched bipedalism practiced by other apes, such as chimps.
Full bipedalism, thus, would have made our hominin ancestors well adapted to withstand the rigours of long journeys.
“The data suggest that by this time in our evolutionary history, selection for reduced energy expenditures during walking was strong,” says Raichlen.
“This work suggests that, by 3.6 million years ago, climate and habitat changes likely led to the need for ancestral hominins to walk longer distances during their daily foraging bouts. Selection may have acted at this time to improve energy economy during locomotion, generating the human-like mechanics we employ today.”