Foot fossil shows ape-like toddler climbed trees 3.3 million years ago

Children from a species related to humans climbed trees more than their parents, researchers announced in study published Wednesday. While the adults primarily walked on two feet like humans do today, 3.3 million years ago children exhibited some ape-like qualities that allowed them to venture up trees. 

Researchers have been studying the fossil of a female toddler younger than three years old, called Selam, since it was discovered in Ethiopia in 2002. Most recently, researchers studying Selam’s foot discovered the toddler had ape-like qualities, such as curved finger and toe bones, not as prevalent in Australopithecus afarensis adults — an extinct human species related to homo sapiens. 

“For the first time, we have an amazing window into what walking was like for a 2½-year-old, more than 3 million years ago,” said Jeremy DeSilva, lead study author and an associate professor of anthropology at Dartmouth College, in a statement. “This is the most complete foot of an ancient juvenile ever discovered.”

The foot, exceptionally rare due to its age and the age of its owner, demonstrates how the species’ bodies changed as they grew into adults and what that change says about the environment they grew up in. The species at that time were small with body hair and brain size similar to chimpanzees, according to  

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Selam also represents species at the “cusp” of being human, according to the researchers. The foot, about the size of a human thumb, represents the transitional space A. afarensis occupied in evolution  — not quite reaching humans’ ease walking on two feet but also not far off. 

 The structure of A. afarensis’ hips and legs are so similar to humans researchers are confident they walked on two legs. In the bone structure of the foot, the difference in the base of the big toe in adults and children is what led researchers to realize children spent more time climbing than their parents. The toe bones in children are curved while adults are not, meaning kids could walk upright but also gripped either trees or their mothers, researchers found.

“If you were living in Africa 3 million years ago without fire, without structures, and without any means of defense, you’d better be able get up in a tree when the sun goes down,” DeSilva said in a statement. 



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