Fossils show flat-footed humans weren't such monkeys after all

Published on Monday 13 April 2009 22:08

OUR ancestors may not be the monkey-like creatures they are traditionally shown as, a study claims.

Scientists who studied the ankle joints of ancient humans, known as "hominins", found they were terrible at climbing trees.

The creatures lived a relatively short time after what became humans and chimpanzees split from a common ancestor four to eight million years ago.

Many experts previously suggested the creatures were primate-like. As a result it has been widely assumed that the earliest humans were ape-like too.

But the latest research suggests that, unlike modern chimps, hominins were not built to scale trees.

The discovery was made by Dr Jeremy DeSilva and his team at the University of Michigan.

After analysing the skeletal motion of chimpanzees Dr DeSilva found the angle of dorsiflexion – the degree to which the ankle rotates to point the toes upwards – was far more extreme in early chimps than in human ancestors.

It showed that chimpanzees were capable of a 45-degree bend, whereas the range in humans was between 15 and 20 degrees.

To assist steeper levels of dorsiflexion in chimps, the bottom of the tibia – the larger of the two bones in the lower leg – is shaped in a certain way where it joins the ankle.

But of the 12 fossil hominin tibias Dr DeSilva examined, no such adaptation was found. It indicates that early humans could not have been good climbers.

Dr DeSilva wrote in the journal Proceedings of the National Academy of Sciences: "Early hominins may have climbed trees like modern humans can and occasionally do today. However, this study suggests that vertical climbing and arboreality were not significant parts of their locomotor repertoire."

While there has been little debate that man shares ancestry with modern apes, the research suggests humans may have had less in common with primates at an earlier stage of development.

Dr Bill Sellers, a primatologist from the University of Manchester, described the findings as "interesting".

He said that, although he had always believed early hominins were quite human-like, some scientists disagreed with the comparison.

"There's a big argument as to how human-like these very early human ancestors were," he said.

"It seems as though Dr DeSilva has been doing an analysis of the existing fossil evidence for this period and his conclusions are suggesting these are more like the modern human than we previously thought."

He added: "It is interesting because the current feeling is that (our evolution] was at a half-way stage at that point. If he is showing a very human-like ankle that early, that would push back the time for very upright human-like walking."

Dr Sellers told The Scotsman he had always believed hominins were more human-like than ape-like at that time. However, he said it would surprise other scientists.

He said the ankles of hominins were crucial for understanding how humans developed. If they spent their time on the ground, like humans, their feet would be in a bent position. But if they spent their time climbing trees, the ankle joint would become a very different shape.

"That's why people are so interested in this very early change," he added.

"What would solve the argument is if we could find a four-million-year-old foot. That would provide the answer."