Evolution charts showing the change from primate to human over millions of years could one day include a close-up of the hands.

Three Stony Brook University researchers published a paper in the journal Nature Communications on Tuesday citing evidence that the hands of chimpanzees and orangutans have undergone more changes and adaptations than ours.

"Human hands have not changed that much since they diverged from chimpanzees," said Sergio Almécija, a paleo-anthropologist and lead author of the study. "Chimpanzees have actually evolved more than humans."

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The researchers measured hand proportions -- the thumb in relation to the fingers -- in humans, living and fossil apes, and fossils of early human ancestors dating back between 1.9 million and 4.4 million years ago.

What they found was that fingers of chimpanzees and orangutans elongated over time while those of humans, human ancestors and gorillas showed very little change.

"Humans are actually more primitive in terms of hand proportions," said Almécija, who earlier this month became an assistant anthropology professor at the Center for the Advanced Study of Human Paleobiology at The George Washington University in Washington.

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Those elongated digits came with a reason. Chimpanzees can move from branch to branch below the tree line using only their arms, a form of travel known as brachiating, said April Truitt, co-founder and executive director of Primate Rescue Center Inc., a federally licensed and inspected sanctuary in central Kentucky that is home to 11 chimpanzees.

"It's mostly used as a transport means or an escape means," Truitt said. "Their hands are incredibly useful to them."

At the sanctuary, monkeys and chimpanzees often are given mostly finished peanut butter jars. The monkeys will rip into them but the chimpanzees will screw off the tops, she said. "Their hands are shaped like hooks that can be very helpful for them."

As for their smaller thumbs?

"They're sort of rudimentary," Truitt said. "They don't make as big a deal out of them. They don't use them a lot."

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Not so for humans. But Almécija posits that perhaps what led humans to success with early tools was not just because of their long thumbs. "Their hands were probably much like ours today," he said. "It was probably more an increase in cognitive capabilities."

To be fair, Almécija points out that walking upright, enlarged heads, changed faces and new hair patterns are all proof of human evolution.

"I'm not saying humans in general are more primitive," he said. "I'm saying, for the case of the hands, that seems to be the case."

"Evolution just means change over a long time. It doesn't mean good or bad."