Most
of us walk and carry items in our hands every day. These are seemingly
simple activities that the majority of us don’t question. But an
international team of researchers, including Brian Richmond at the
George Washington University, have discovered that human bipedalism, or
walking upright, may have originated millions of years ago as an
adaptation to carrying scarce, high-quality resources. This latest
research was published in this month’s Current Biology.
The
team of researchers from the U.S., England, Japan and Portugal
investigated the behavior of modern-day chimpanzees as they competed for
food resources, in an effort to understand what ecological settings
would lead a large ape – one that resembles the 6 million-year old
ancestor we shared in common with living chimpanzees—to walk on two
legs.
“These
chimpanzees provide a model of the ecological conditions under which
our earliest ancestors might have begun walking on two legs,” said Dr.
Richmond, an author of the study and associate professor of anthropology
at GW’s Columbian College of Arts and Sciences. “Something as simple as
carrying—an activity we engage in every day—may have, under the right
conditions, led to upright walking and set our ancestors on a path apart
from other apes that ultimately led to the origin of our kind.”
The
research findings suggest that chimpanzees switch to moving on two
limbs instead of four in situations where they need to monopolize a
resource, usually because it may not occur in plentiful supply in their
habitat, making it hard for them to predict when they will see it again.
Standing on two legs allows them to carry much more at one time because
it frees up their hands. Over time, intense bursts of bipedal activity
may have led to anatomical changes that in turn became the subject of
natural selection where competition for food or other resources was
strong.
Two
studies were conducted by the team in Guinea. The first study was in
Kyoto University’s “outdoor laboratory” in a natural clearing in Bossou
Forest. Researchers allowed the wild chimpanzees access to different
combinations of two different types of nut—the oil palm nut, which is
naturally widely available, and the coula nut, which is not. The
chimpanzees’ behavior was monitored in three situations: (a) when only
oil palm nuts were available, (b) when a small number of coula nuts was
available, and (c) when coula nuts were the majority available resource.
When
the rare coula nuts were available only in small numbers, the
chimpanzees transported more at one time. Similarly, when coula nuts
were the majority resource, the chimpanzees ignored the oil palm nuts
altogether. The chimpanzees regarded the coula nuts as a more
highly-prized resource and competed for them more intensely.
In
such high-competition settings, the frequency of cases in which the
chimpanzees started moving on two legs increased by a factor of four.
Not only was it obvious that bipedal movement allowed them to carry more
of this precious resource, but also that they were actively trying to
move as much as they could in one go by using everything available—even
their mouths.
The
second study, by Kimberley Hockings of Oxford Brookes University was a
14-month study of Bossou chimpanzees crop-raiding, a situation in which
they have to compete for rare and unpredictable resources. Here, 35% of
the chimpanzees’ activity involved some sort of bipedal movement, and
once again, this behavior appeared to be linked to a clear attempt to
carry as much as possible at one time.
