WASHINGTON, July 15 (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.
Writing in the journal Neurosurgical Focus on Sunday, Filler said one
main clue was a bone feature called the transverse process, which sticks
out from the side of the hollow, round vertebrae, Filler said in a
telephone interview. This is where muscles attach to the spine.
"The vertebra is transformed in a way that literally reverses the
mechanics of the spine," Filler said. "The bone lever of the vertebrae gets
switched from bending the spine forward to bending the spine back."
Most vertebrates are oriented forward, to walk on all fours. The
transverse process is at the front of each vertebra, facing the animal's
belly. This is true of monkeys, too.
But in humans and in the 21 million-year-old fossil of a creature
called Morotopithecus bishopi, a tree-dwelling, ape-like creature that
lived in what is now Uganda, the transverse process has moved backward,
behind the opening for the spinal cord.
Great apes, such as chimpanzees, share this feature.
'THE UPRIGHT APE'
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.
In his study and in a book published last week called "The Upright
Ape -- a new origin of the Species," Filler argues that this common
ancestor, and ancestors going back many millions of years before, walked
upright. Homo sapiens, the human species, continued upright, while apes
evolved back toward all fours, he argues.
"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.
