Hominins were walking like Homo sapiens earlier than scientists thought

April 23 (UPI) -- Early hominins had adopted a human-like gait prior to the emergence of the Homo genus, new research suggests.

After analyzing a series of 3.6-million-year-old hominin footprints, researchers determined human-like bipedalism evolved much earlier than previously thought.

"Fossil footprints are truly the only direct evidence of walking in the past," David Raichlen, an associate professor at the University of Arizona, said in a news release. "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."

The earliest species from the genus Homo, including Homo habilis and Homo erectus, emerged between 2 and 2.5 million years ago. Species that preceded the genus are often referred to collectively as hominins.

Scientists believe hominins began walking on two feet as early as 7 million years ago, but that their crouched shuffle recalled the bent-legged walk of their ape ancestors more than the upright gait of modern humans.

In an effort to more accurately characterize the posture and stride of early hominins, researchers analyzed the depth and shape of ancient footprints left at Tanzania's famed Laetoli site.

By comparing the depth of the impression left by the toe versus the heel, scientists were able to model the movement of the center of mass during the step. The analysis, presented over the weekend at the Experimental Biology conference in San Diego, suggests hominins walked more upright than previously thought, leaving behind a footprint similar to modern humans.

Researchers believe a more upright walk allowed early hominins to travel farther in search of food and expend less energy doing so.

"The data suggest that by this time in our evolutionary history, selection for reduced energy expenditures during walking was strong," said 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."