July 15, 2007 / 4:06 AM / 12 years ago

Blame that bad back on your ancestors

WASHINGTON (Reuters) - A spine specialist trying to figure out why people so often have bad backs says he has come up with a new theory about when and how early humans evolved the ability to walk upright.

The uncannily human-looking backbone of a 21 million-year-old precursor of humans and apes gives the first clue, said Dr. Aaron Filler of the Cedars Sinai Medical Center in Los Angeles.

A major change in the vertebrae that allowed this pre-human to stand upright and carry things also made it easier to crush and strain the spongy discs between each vertebra, Filler, a medical doctor with a doctorate in anthropology proposes.

That, in turn, explains why back pain is a leading cause of disability, he said.





Great apes, such as chimpanzees, share this feature.


The fossil was discovered in the 1960s but no one noticed the important change until 1997, when paleontologist Laura MacLatchy of the State University of New York at Stony Brook reported on the remarkable features of Morotopithecus.

“That means that upright posture bipedalism goes back 20 million years, not just 5 or 6 million years,” said Filler.


“When you look at most ape species, their spines and most of their bodies still look pretty monkey-like,” Filler said.

He also said humans evolved a new structure of muscles that pull the body from side to side while standing.

“This is very important for carrying an infant or child,” Filler said. “From the point of view of back pain, now we have big muscles doing this heavy work that never did before. They can get torn and strained.”

The backward orientation also allows the cushiony discs to get crushed, Filler said. “In most animals the vertebrae get spread apart when they carry infants on their backs when on all fours,” he said.

What further differentiates humans from apes is the positioning of the place where the spine attaches to the hips, said Filler, who dissected the backbones of dead gibbons, chimpanzees and macaque monkeys and compared them to bones from living and extinct species of other animals and fossils from various pre-humans.

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