Baby steps suggest our ancestors liked trees
The oldest complete human-like foot yet discovered suggests that our ancestors spent much of their childhoods clinging to trees, scientists say.
The fossil belonged to the Dikika child, a toddler about two-anda-half years old, similar in size to a chimpanzee of comparable age, who lived in what is now northern Ethiopia about 3.3 million years ago.
Like Lucy, a more famous specimen from about 200,000 years later, the little girl came from a hominin species called Australopithecus afarensis, which straddled the blurry divide between canopy-dwelling apes and bipedal humans.
When the Dikika child’s skeleton was dug up in 2000, her left foot was buried in sediment and had to be prised out with extreme care.
The whole thing is a mere 5.5cm long, or about as big as a modern human adult’s thumb.
It is only now that palaeontologists have been able to examine the nuances of its shape for hints about how she might have walked.
The results, published in the journal Science Advances, strongly suggest that her body was adapted for life in the trees, although she would probably have spent more time on the ground as she grew up. She was, in other words, a link between the apes and the first humans.
Jeremy DeSilva, associate professor of anthropology at Dartmouth College in Hanover, New Hampshire, and the paper’s lead author, said the Dikika child would have been much safer if she could nimbly climb trees.
‘‘If you were living in Africa three million years ago without fire, without structures, and without any means of defence, you’d better be able to get up in a tree when the sun goes down,’’ he said.
In many ways the child’s foot resembles those of her elders.
The foot had a low arch and a large heel bone that would have made it much easier to walk on two legs without getting injured, although it would not have been robust enough to sustain long bouts of running.
The structure of her big toe, however, is a little more like a chimp or a gorilla.
The bone at its base, the medial cuneiform, is curved slightly outwards, meaning that she would have been able to oppose her toes and grip branches with a fair degree of dexterity.
The researchers think she was probably carried around by adults much of the time, but would have been able to shin up the trunk of a tree for food or shelter if necessary.