It turns out that our shoulders may be more evolved. Scientists have taken a closer look at the human shoulder in order to better understand evolution.

"Humans are unique in many ways," said Nathan Young, one of the researchers, in a news release. "We have features that clearly link us with African apes, but we also have features that appear more primitive, leading to uncertainty about what our common ancestor looked like. Our study suggests that the simplest explanation, that the ancestor looked a lot like a chimp or gorilla, is the right one, at least in the shoulder."

Humans split from our closest African ape relatives about 6 to 7 million years ago. Certain human traits, though, resemble the more distantly related orangutan or even monkeys. This combination of characteristics calls into question whether the last common ancestor of modern humans and African apes looked more like modern day chimps or gorillas or an ancient ape unlike any living group.

The shoulder shape actually tracks changes in early human behavior, such as reduced climbing and increased tool use. The shoulders of African apes, for example, consist of a trowel-shaped blade and a handle-like spine that points the joint with the arm up toward the skull, giving an advantage to the arms when climbing or swinging through the branches. In contrast, the scapular spine of monkeys is pointed more downwards, and this trait is even more pronounced in humans.

The researchers compared 3D measurements of fossil shoulder blades of early humans and modern humans against African apes, orangutan, gibbons, and large, tree-dwelling monkeys. In the end, the researchers found that australopiths were intermediate between African apes and humans. A. afarensis shoulders were more like an African ape than a human, and A. sediba shoulders were closer to a human's than to an ape's.

The findings reveal a bit more about human evolution, and also show a bit more about human shoulders today. This could potentially help researchers identify which areas in the shoulder are most prone to injury, and people can do strength exercises to protect those parts.

The findings are published in the journal Proceedings of the National Academy of Sciences.

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