WASHINGTON - 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
That, in turn, explains why back pain is a leading cause of disability, he
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
"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