Human Foot Not So Special After All, Study Finds

The human foot may not be all that special after all, a new study conducted by researchers at the University of Liverpool found.

After studying more than 25,000 human steps taken on a pressure-sensitive treadmill, the scientists discovered that, despite having long abandoned life in the trees, humans' feet still retain a degree of flexibility similar to that seen in the feet of great apes, including orangutans and chimpanzees, who have remained tree-dwelling to this day.

The finding stands in open opposition to current theories based on research carried out in the 1930s in which scientists argued that human feet function in a radically different way than apes as a result of the development of arches in the midfoot and the believed rigidity of their outside edge.

"It has long been assumed that because we possess lateral and medial arches in our feet -- the lateral one supposedly being rigid and supported in bone -- that our feet differ markedly to those of our nearest relatives, whose mid-foot is fully flexible and makes regular ground contact," said Robin Crompton from the school's Institute of Ageing and Chronic Disease.

However, this presumed singularity was never quantitatively tested, Crompton explains.

Sure enough, in the course of their research the team determined "that the range of pressures exerted under the human [midfoot], and thus the internal mechanisms that drive them, were highly variable, so much so that they actually overlapped with those made by the great apes."

The discovery coincides with a growing body of research that demonstrates that some healthy individuals produce footfalls in which the midfoot touches the ground as they walk -- a phenomenon previously believed to only occur in individuals with diabetes or arthritis.

"Our ancestors probably first developed flexibility in their feet when they were primarily tree-dwelling, and moving on bendy branches, but as time passed and we became more and more ground-dwelling animals, some new features evolved to enable us to move quickly on the ground," said Karl Bates, also from the Institute of Ageing and Chronic Disease.

However, Bates explains, humans' limbs "did not adapt to life on the ground anywhere near as much as those of other ground-dwelling animals such as horses, hares and dogs."

One possible reason for this retained flexibility of the foot is the increased ability to navigate a variety of surfaces it offers, the researchers hypothesize.

"The next part of our study will be testing this theory, which could offer a reason why humans can outrun a horse, for example, over long distances on irregular terrain," Bates said.