![]() “The mix of ape and human features observed in A. This positioning is consistent with evidence for increasingly sophisticated tool use in Australopithecus. sediba closer to human’s than to an ape’s. afarensis shoulder was more like an African ape than a human, and A. The results showed that australopiths were intermediate between African apes and humans: the A. “Finding fossil remains of the common ancestor would be ideal, however, when fossils are absent, employing such multifaceted techniques is the next best solution,” said Zeray Alemseged, PhD, senior curator of Anthropology at the California Academy of Sciences. ergaster and Neandertals, to see where they fit on the shoulder spectrum. To find out, Young and his team analyzed two early human Australopithecus species, the primitive A. “How did the human lineage evolve and where did the common ancestor to modern humans evolve a shoulder like ours?” Primitive in some ways, derived in other ways, and different from all of them,” Young said. “Human shoulder blades are odd, separated from all the apes. They found that the modern human’s shoulder shape is unique in that it shares the lateral orientation with orangutans and the scapular blade shape with African apes a primate in the middle. The researchers tested these competing theories by comparing 3-D measurements of fossil shoulder blades of early hominins and modern humans against African apes, orangutan, gibbons and large, tree-dwelling monkeys. The prevailing question was whether humans evolved this configuration from a more primitive ape, or from a modern African ape-like creature, but later reverted back to the downward angle. In humans this trait is even more pronounced, indicating behaviors such as stone tool making and high-speed throwing. In contrast, the scapular spine of monkeys is pointed more downwards. The shoulders of African apes 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. The paper, titled Fossil Hominin Shoulders Support an African Ape-like Last Common Ancestor of Chimpanzees and Humans, published online Sept. It appears, he said, that shoulder shape tracks changes in early human behavior such as reduced climbing and increased tool use. “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.” ![]() 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,” said Nathan Young, PhD, assistant professor at UC San Francisco School of Medicine and lead author of the study. This combination of characteristics calls into question whether the last common ancestor of modern humans and African apes looked more like modern day chimps and gorillas or an ancient ape unlike any living group. Yet certain human traits resemble the more distantly related orangutan or even monkeys. Humans split from our closest African ape relatives in the genus Pan – including chimpanzees and bonobos – 6 to 7 million years ago. ![]() ![]() A new study led by researchers at UC San Francisco shows that important clues lie in the shoulder. But what this last common ancestor with apes looked like has remained unclear. As early humans increasingly left forests and utilized tools, they took an evolutionary step away from apes. ![]()
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