Human-Evolution
Sergio Almecjia (above left) and William Jungers used primitive skeletal databases from different institutions to study the changes of hand proportions over the last millions of years.  PHOTO CREDIT: SBU

Every few weeks, Kenneth Wengler, a graduate student studying biomedical engineering, will take a look at Stony Brook-related science and research news.

Hands have been one of humans’ most prized assets. The opposable thumb has given them the evolutionary advantage over other species for millennia and their ability to use tools allowed them to build the civilizations seen today. It has long been believed that the human hand evolved to better use tools, and this is what separated the species from its ape cousins.

But a recent study by Stony Brook University researchers has found that the human hand is less evolved than that of humans’ closest living evolutionary relatives. The researchers are Sergio Almecjia, a professor at the Center for the Advanced Study of Human Paleobiology at George Washington University and a former post-doc in the Department of Anatomical Sciences at Stony Brook University School of Medicine, and William Jungers, a professor in the Department of Anatomical Sciences at Stony Brook University School of Medicine.

“The human is not that different from other ancestral apes, but it is chimpanzees and other modern apes whose hands have changed more over time,” Almecjia said. “Chimpanzees and other apes have elongated their digits over time to better hang from the branches of trees. Our thumbs have elongated a little bit and our digits have shortened a little bit to better grip tools, but the change is much less compared to other living primates.”

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Almecjia and Jungers used primate skeletal databases from institutions across the United States and Europe to study the changes of hand proportions over the last 20 million years. The study included 274 primates from 34 different species and used a ratio of thumb-to-digit length to compare the hands.

“I was looking at the hands of apes from years before humans and chimpanzees separated,” Almecjia said. “And looking at human hands and chimpanzee hands, it looked like human hands weren’t so different, but it was the chimpanzee hands that looked odd.”

Until recently, the major hypothesis for the cause of human hand evolution has been the use of stone tools. Studies such as this are beginning to question the antiquated theory and shed light on how primate hands had already evolved to facilitate the use of tools over 3 million years before the appearance of stone tool making.

“We have assumed over the years that humans have changed a lot over time,” Almecjia said. “Our hand is so different from chimpanzees because we had evolved our hands to better use tools. Primitive human hands were pretty much like our hands today, and this doesn’t explain humans using tools. Instead it could have been due to changes of our brain.”

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Correction: Sept. 11, 2015

A previous version of this story erroneously reported the last name of one of the researchers. His name is Sergio Almecjia, not Sergio Almencjia.

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