How the human race stands on some big and ancient shoulders

The evolution of the shoulder helps explain how humans were able to become great throwers, 'turning our species into the most dominant predators on earth.'

Abbas Dulleh/AP
A caretaker interacts with a chimpanzee after feeding time, on the six mangrove outcroppings that make up Chimpanzee Island, about 31 miles southeast of Liberia’s capital, Monrovia, Aug. 18.

The latest evolutionary clues linking humans to our last common ancestor with apes lie in the shoulder, according to a new study released this week.

“Humans split from our closest African ape relatives in the genus Pan – including chimpanzees and bonobos – 6 to 7 million years ago,” researchers at the University of California San Francisco said in a statement. “Yet certain human traits 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 and gorillas or an ancient ape unlike any living group.”

The correct explanation also happens to be the simplest – that the ancestor most resembled a chimp or gorilla, said Nathan Young, lead author of the study, in the release. “At least in the shoulder.”

Results of the study were published Monday in the journal PNAS. The researchers found that the shape of the shoulder could track changes in early human behavior, such as reduced climbing and increased tool use, Dr. Young said.

For example, “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,” said the team.

“In contrast, the scapular spine of monkeys is pointed more downwards. In humans this trait is even more pronounced, indicating behaviors such as stone tool making and high-speed throwing,” the study found.

Researchers set out to determine whether humans have evolved “from a more primitive ape, or from a modern African ape-like creature.”

The team used 3-D measurements of fossil shoulder blades from early hominins – modern humans and our ancestors – to compare against different types of apes and monkeys.

What they found was 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,” said researchers.

The evolution of the shoulder is also significant in explaining how humans are able to throw objects with speed and accuracy, said Neil T. Roach, a fellow of human evolutionary biology at Harvard University.

A laterally facing shoulder blade, for instance, also serves as an energy reserve for humans, “much like a slingshot, facilitating high-speed throwing,” according to the statement.

“These changes in the shoulder, which were probably initially driven by the use of tools well back into human evolution, also made us great throwers,” Dr. Roach said. “Our unique throwing ability likely helped our ancestors hunt and protect themselves, turning our species into the most dominant predators on earth.”

You've read  of  free articles. Subscribe to continue.

Dear Reader,

About a year ago, I happened upon this statement about the Monitor in the Harvard Business Review – under the charming heading of “do things that don’t interest you”:

“Many things that end up” being meaningful, writes social scientist Joseph Grenny, “have come from conference workshops, articles, or online videos that began as a chore and ended with an insight. My work in Kenya, for example, was heavily influenced by a Christian Science Monitor article I had forced myself to read 10 years earlier. Sometimes, we call things ‘boring’ simply because they lie outside the box we are currently in.”

If you were to come up with a punchline to a joke about the Monitor, that would probably be it. We’re seen as being global, fair, insightful, and perhaps a bit too earnest. We’re the bran muffin of journalism.

But you know what? We change lives. And I’m going to argue that we change lives precisely because we force open that too-small box that most human beings think they live in.

The Monitor is a peculiar little publication that’s hard for the world to figure out. We’re run by a church, but we’re not only for church members and we’re not about converting people. We’re known as being fair even as the world becomes as polarized as at any time since the newspaper’s founding in 1908.

We have a mission beyond circulation, we want to bridge divides. We’re about kicking down the door of thought everywhere and saying, “You are bigger and more capable than you realize. And we can prove it.”

If you’re looking for bran muffin journalism, you can subscribe to the Monitor for $15. You’ll get the Monitor Weekly magazine, the Monitor Daily email, and unlimited access to