The ancestors of humanity are often depicted as knuckle-draggers,
humans seem unusual in our family tree as "upright apes."
Controversial research now suggests the ancestors of humans and the
great apes might have actually walked upright too, making
chimpanzees and gorillas the exceptions and not the rule.
In other words, "the other great apes we see now, such as chimps
or orangutans, might have descended from human-like ancestors,"
Aaron Filler, a Harvard-trained evolutionary biologist and medical
at Cedars-Sinai Institute for Spinal Disorders in
Los Angeles , told
Filler analyzed how the spine was assembled in more than 250 living and
extinct mammalian species, with some bones dating up to 220 million
He discovered a series of changes that suggest walking upright-and not
our knuckles-might actually have been the norm for the ancestors of
In most creatures with a backbone, the body is separated roughly in
a tissue structure that runs in front of the spinal canal. This
septum" divides the body into a dorsal part (corresponding to the
of humans), and a ventral part (or the front half).
A strange birth defect in what may have been the first direct human
led this septum to cross behind the spinal cord in the lumbar or lower
region-an odd configuration more typical of invertebrates. This would
made horizontal stances inefficient.
"Any mammal with this set of changes would only be comfortable
upright," Filler said. "I would envision this malformed young
'hominiform' -the first true ancestral human-as standing upright
from a young
age," he added, while the rest of the mutant's family and species
to walk around "on all fours."
This change to an upright posture could have occurred "very
just a few shifts in 'homeotic' genes, or ones responsible for how the
plan is laid out," Filler said.
The earliest known bipedal apes-those walking on two legs-were thought
date back as far as some 6 million years or so. Now Filler's new
suggest the earliest upright ape known so far was the extinct hominoid,
Morotopithecus bishopi, which lived in
Uganda more than 21 million years
"Humanity can be redefined as having its origin with
Morotopithecus, " Filler
said. He detailed his findings online Oct. 10 in the journal PLoS ONE.
This research pushes back the date for the origins of bipedalism
million years, to before the last common ancestor of humans, chimps,
gorillas and orangutans, as well as lesser apes such as gibbons. The
match up with recent findings that suggest upright walking might have
started before humanity's ancestors even left the trees.
"If you look at baby siamangs, which are a kind of gibbon, you'll
walk bipedally on their own," Filler said. "It's just their
natural way of
walking. They never knuckle walk."
If bipedalism did evolve 21 million years ago, it more likely evolved
walk in trees than on the ground, said
University of Chicago
anthropologist Russell Tuttle. "Twenty-one million years ago,
there were a
lot of trees around," he said.
Besides Morotopithecus, fossil vertebrae suggest three other upright
species precede the 6 million year mark, Filler added.
"So you have this fossil evidence for bipedalism, and you have
apes such as
gibbons," he said. "Perhaps humans represent the primitive
knuckle walkers such as chimps and gorillas are modified."
The ancestors of chimps and gorillas might have evolved knuckle walking
speedier mode of travel, Filler suggested. If bipedalism did come first,
that means gorillas and chimpanzees might have evolved knuckle walking
independent of each other. Future analysis of the genes of those apes
show they came across knuckle walking in different ways, supporting
"I am getting the feeling that a revolution in our thinking about
origins of bipedality is now under way," said evolutionary
Robin Crompton at the University
of Liverpool in