Why Our Early Human Ancestors Took to Two Feet: Evolution of Walking

Why did humans decide to walk on two feet? Good question--and now we may have an answer. Researchers may have discovered how our earliest ancestors developed the ability to walk upright instead of dwelling in trees.

In order to examine the origins of our two-legged stride, researchers looked at the ancient terrain of East and South Africa. Shaped during the Pliocene epoch by volcanoes and shifting tectonic plates, this landscape was rugged with rocky outcrops and gorges. It's very possible that hominins, our early forebears, were attracted to this terrain since it offered both shelter and opportunities to trap prey.

"Our research shows that bipedalism may have developed as a response to the terrain, rather than a response to climatically-driven vegetation changes," said Isabelle Winder of the Department of Archaeology at New York in a news release. "The broken, disrupted terrain offered benefits for hominins in terms of security and food, but it also proved a motivation to improve their locomotor skills by climbing, balancing, scrambling and moving swiftly over broken ground-types of movement encouraging a more upright gait."

As our early ancestors began to walk and scramble across the rocky landscape, though, they also developed in other ways. Their hands and arms were left free as they trekked across the terrain. This, in turn, allowed them to increase manual dexterity and tool use. In other words, bipedalism encouraged further development and may have led to a key stage in the evolutionary story of our ancestors.

While hominins learned to walk, though, running wasn't possible until much later. The movement was probably awkward at first. Yet researchers believe that it too was probably inspired by the landscape. It's possible that running adaptations to the skeleton and foot may have resulted from excursions into the surrounding flat plains in search of prey and new home ranges.

"The varied terrain may also have contributed to improved cognitive skills such as navigation and communication abilities, accounting for the continued evolution of our brains and social functions such as cooperation and team work," said Winder. "Our hypothesis offers a new, viable alternative to tradition vegetation or climate change hypotheses."

The findings are published in the journal Antiquity.