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 McClatchy 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.
