Have you ever wondered how humans evolved from walking on all fours to walking upright on two legs? A new study of a 6-million-year-old ape fossil is providing important clues about the origins of human bipedalism.

Us and our closest relatives, apes, show a diversity of ways of getting around – from walking upright to climbing trees and walking on all fours. Scientists have long wondered how humans evolved from four-legged ancestors to have upright posture and two-legged walking. But past studies and fossil records did not give a clear picture of the early stages.

The new study focuses on recently discovered skulls of an ancient ape called Lufengpithecus that lived 6 million years ago. Using a special 3D scanning technique on the skulls, researchers were able to look inside the bony region of the inner ear for the first time. This provided clues about how these extinct apes moved.

The inner ear has fluid-filled canals called semicircular canals that help provide our sense of balance and position when we move. We were able to visualize the internal structure of fossil skulls and study details of the semicircular canals to reveal how extinct mammals moved, says study author Yinan Zhang.

The size and shape of the canals relates to how mammals – including apes and humans – get around. The scans of Lufengpithecus showed it had a mix of climbing, hanging from branches, tree climbing, and some walking on two and four legs.

Based on this, the researchers believe human bipedalism evolved in three stages. First, very early apes moved through trees like gibbons do today. Second, the common ancestor of apes and humans had a varied style of movement like Lufengpithecus. Finally, full human bipedalism evolved from this flexible ancestral style of locomotion.

Previous studies looked mostly at bone structures, but the diversity of living apes and incomplete fossil records made the timeline unclear. Lufengpithecus provides a unique chance to look at locomotion evolution in new ways, says project leader Professor Xijun Ni. The inner ear may preserve a singular record of ape mobility history.

This study suggests early apes shared movement abilities related to later human bipedalism. It shows how environmental changes like cooling climates may have driven increased diversity and faster evolution in ape and human locomotion over time. The inner ears of fossil apes are giving scientists new clues to understand our distant ancestors and how humans came to walk upright.


New York University | Yinan Zhang et al., Lufengpithecus inner ear provides evidence of a common locomotor repertoire ancestral to human bipedalism, The Innovation (2024). DOI: 10.1016/j.xinn.2024.100580

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