Our ape ancestors might have been more versatile than we’ve given them credit for. A study of modern gorillas suggests that the common ancestor we share with them may have been able to walk in a variety of ways, not just one or two.
Within the last 20 million years, our ancestors split from those of orangutans. Later, we also branched off from the African great apes: first gorillas, then chimpanzees and bonobos. However, we do not know what our common ancestors with these species looked like.
One long-standing question is how our ape ancestors moved around, because understanding that would help us understand how our two-legged method of walking evolved.
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For many years, it was thought that the common ancestors were knuckle-walkers: they walked on all fours, putting much of their weight on the knuckles of their hands. However, more recent evidence suggests that bipedalism evolved early, in the tree-dwelling ancestor we share with orangutans, and not out of knuckle-walking.
Now it is being suggested that our ape ancestors had many options at their disposal.
Nimble walkers
A team led by of the George Washington University set up high-speed cameras to track mountain gorillas () in the forests of Uganda and Rwanda. Over 7 weeks, they filmed 77 gorillas: 8 per cent of the known population.
Gorillas are normally classed as knuckle-walkers. In line with this, knuckle-walking was seen most often: 61 per cent used only this method.
However, the remaining 39 per cent also walked in other ways. They flattened the backs of their hands against the ground, “fist-walked” by resting on a different part of the fingers, and even used their palms. The latter two have previously only been anecdotally reported in gorillas, but are common among orangutans.
In light of this, the researchers argue that the common ancestor of humans and African apes – and possibly also the common ancestor of all great apes – could walk in a variety of ways.
On your feet
Experts on human evolution have welcomed the findings, but some question Almécija’s interpretation.
The findings are a reminder that neat categories, like gorillas being knuckle-walkers, are rare in biology, says of George Washington University. That rule of thumb will apply to our extinct ancestors as well. “We need to get out of the bad habit of thinking that the only options for ancestral modes of locomotion are the simple categories embraced by conventional wisdom.”
However, there is no indication of knuckle-walking in the human ancestral fossil record, says of the University of Liverpool, UK. As a result, most researchers agree that the common ancestor was not a pure knuckle-walker. “The majority of people working in locomotion research have rejected that idea a long time ago.”
Instead, it may be that gorillas only evolved the other walking styles recently, perhaps as a result of crossing mountainous terrain. “To test this possibility we need to perform similar studies in western gorillas, as well as in chimpanzees, bonobos and orangutans,” says Almécija. However, he says his hunch is that “these are primitive postures common to all the great apes”.
Ultimately, we may not be able to figure out what the common ancestor was like by studying living species, says of Washington University in St. Louis. “This question is ultimately only going to be resolved by discovering more and better fossils that branched off near the origins of the chimpanzee, gorilla and human lineages.”
American Journal of Physical Anthropology
