http://news.liv.ac.uk/2013/08/20/human-foot-not-as-unique-as-originally-thought/

In a study of more than 25,000 human steps made on a
pressure-sensitive treadmill at the University’s Gait Laboratory, scientists at
Liverpool have shown that despite having abandoned life in the trees long ago,
our feet have retained a surprising amount of flexibility, the type seen in the
feet of other great apes, such as orang-utans and chimpanzees, that have
remained largely tree-dwelling.

It has previously been thought that humans who make contact with the ground with
the mid-foot region are primarily those that suffer from diabetes or arthritis,
both of which can impact on the structure of the feet. Research showed, however,
that two thirds of normal healthy subjects produced some footfalls where the
mid-foot touches the ground, with no indication that this is other than an
aspect of normal healthy walking.

"We hypothesise that despite becoming nearly exclusively ground dwelling we have
retained flexibility in the feet to allow us to cope effectively with the
differences in hard and soft ground surfaces which we encounter in long distance
walking and running. 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."

Thanks to Rich Lovelace.