There was a common ancestor of humans and African apes in the genus Pan. Humans split from our closest ape relatives about 6-7 million years ago. No one knows what the ancient creature looked like, at least until now. Finding fossils of the common ancestors would have been ideal to reveal what they looked like. In the absence of fossil remains, a group of researchers studied the evolution of the human shoulder to answer that question.

Our last common ancestor resembled a chimp or gorilla

They found that our “last common ancestor” resembled the looks and behavior of a chimpanzee or gorilla, instead of a monkey or orangutan. The study proves that our ancestors climbed down from trees and they were much more evolved that previously thought. When humans split from African apes about 7 million years ago, the first changes were physical because our ancestors had to switch from climbing trees to using tools for survival.

Even though our closest relatives were chimps and bonobos, certain human traits resemble our more distant cousins such as monkeys and orangutans. It raised questions about what the last common ancestor of humans and African apes looked like: modern day gorillas and chimps, or an ancient ape unlike any living group. And some important clues lie in the evolution of the shoulder.

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Nathan Young of the University of California San Francisco, the lead author of the study, said our last common ancestor looked a lot like a chimp or gorilla. The shoulder shape reflects changes in early human behavior like increased tool use and reduced climbing. Findings of the study were published in the journal Proceedings of the National Academy of Sciences (PNAS).

Australopithecus was the common ancestor of apes and humans

After analyzing the shoulder spectrum of a number of species, researchers concluded that the Australopithecus species was the intermediate between African apes and humans. The Australopithecus afarensis was more like an African ape than a human, while Australopithecus sediba was closer to humans than apes.

Young said the human’s shoulder shape shared lateral orientation with orangutans. At the same time, humans’ scapular blade shape resembled that of an African ape. The mix of ape and human features in Australopithecus afarensis suggests that it was a primate “on its way to becoming human.”