Day 23
You should spend about 20 minutes on Questions 14-26, which are based on Reading
Passage 2 below.
When and why did we learn to stand on our own two feet?
We may never know for exactly how long humans have walked on two legs, and the
debate about why we do it continues, but evidence and research give us plenty of clues.
В
For many years, scientists and
anthropologists disagreed about
w hether early humans started
walking on two legs before or after
their brain had increased. The
predominant view was that brain size
was important, and until our brains
had reached a particular size and
mass, bipedal movement would have
been impossible. Then, in 1974, two
scientists, Donald Johanson and
Tom Gray, were mapping a remote
area
of Ethiopia when by chance
they came across some fossilised
bones which appeared to be from
an early human, Australopithecus
afarensis. Excavation of the site led
to the discovery of several hundred
more bones and bone fragments,
all from a single skeleton. Scientific
research of the bones later that year
showed that they were 3.2 million
years old and belonged to a young
fem ale hominid who the scientists
nicknamed ‘Lucy’. Most remarkably,
however, the research showed that
while Lucy had a very small brain
compared with humans today, she
was also bipedal.
How did the scientists know this?
Lucy’s leg bones were angled
relative to the condyles (knee joint
surfaces), which allow bipeds to
balance
on one leg at a time when
walking. There was also a prominent
lip in the knee to prevent the patella
(the knee cap) from dislocating due
to this angle. Evidence was also
found in Lucy’s pelvis, which was
able to accommodate an upright
stance and the need to balance on
only one limb with each stride. The
shape of her ankle also showed that
her big toes would have aligned with
her other toes, which would have
sacrificed manipulative abilities for
efficiency in bipedal locomotion. Her
feet, therefore, would have been
used almost exclusively for getting
around rather than for holding
things. Finally, her backbone showed
evidence of the spinal curvature
necessitated by a permanent upright
stance.
Lucy’s
discovery was exciting for
two reasons. Not only was she
bipedal in spite of her brain size,
but she was also believed to be
our oldest ancestor. However, a
discovery over thirty years later
changed all that. In 2005, Professor
Yohannes Haile-Selassie, head of
Physical Anthropology at Cleveland
Museum of Natural History, led an
Reading Passage 2
international team that discovered
and analysed a 3.6-million-year-old
fossilised partial male skeleton. It
was found in the W oranso-Mille are
of Ethiopia’s A far region, and it took
Professor Haile-Selassie’s team
over five years to excavate. The
team recovered the most complete
shoulder blades ever found in the
human fossil record. A significant
portion
of the rib cage was also
found.
D
It was a significant find because
this early hominid, also a member
of Australopithecus afarensis, is
400,000 years older than Lucy, and
significantly larger in size. Research
on the new specimen revealed that
advanced, human-like bipedalism
occurred much earlier than
previously thought. The specimen
was nicknamed ‘Kadanuumuu’ ,
which means ‘big man’ in the Afar
language and reflects its large size.
The male hominid stood between 1.5
and 1.7 metres tall, while Lucy stood
only 1.1 metres tall. This individual
was fully bipedal and had the ability
to walk almost exactly like modern
humans.
E
Kadanuumuu’s discovery was
important for another reason.
Despite
all the research, there were
still some in the scientific world who
felt there was insufficient proof that
Lucy walked fully upright. ‘AS a
result of our discovery,’ said
Haile-Selassie, ‘we can now
confidently say that Lucy and her
relatives were almost as proficient
walking on two legs as we are,
and that the elongation of our
legs came earlier in our evolution
than previously thought. Until
now, all of our understanding
of Australopithecus afarensis’
locomotion has been dependent on
Lucy Unfortunately, because she
was an exceptionally small female
with very short legs,
this gave some
researchers the impression that
she was not fully adapted to upright
walking. This new skeleton falsifies
that impression because if Lucy’s
frame had been as large as this
specimen, her legs would also have
been proportionally longer.’
F
Professor Haile-Selassie’s research
goes a long way to explain when
humans began walking upright.
However, one tantalising question
remains: why did we start walking
upright? There are several schools
of thought, but two are particularly
compelling. One is that bipedal
activity is linked to the need to carry
as much as possible. ‘Something
as simple as carrying, an activity
we engage in every day, might
have,
under the right conditions,
led to upright walking,’ says Dr
Brian Richmond, who carried out
research on bipedal movement in
apes. ‘Standing on two legs allowed
early humans to carry more at one
time because it freed their hands.’
It is possible to observe this in
apes. While many are capable of
short bursts of bipedal movement,
they only choose to do it when
they need to carry something. And,
interestingly, the more valuable the
object is to them, the more they are
prepared to walk on just two legs in
order to carry it.
G
However, another group of
researchers working at the University
of Arizona has conducted a study
which suggests
that walking upright
is more beneficial because it
Day 23
saves energy. ‘For decades now
researchers have debated the role
and evolution of bipedalism ,’ said
David Raichlen, Assistant Professor
of Anthropology. ‘However, the big
problem in the study of bipedalism
was that there was little data out
there.’ Under his guidance, a group
of researchers at the University
trained five chimpanzees to walk on
an exercise machine while wearing
masks that allowed measurement
of their oxygen consumption. The
chimps were measured both while
walking upright and while moving
on their legs and knuckles. That
measurement of the energy needed
to
move around was analysed
alongside results from similar tests
on humans. Raichlen discovered
that humans walking on two legs
use only one-quarter of the energy
that chimpanzees use while knuckle-
walking on four limbs. And of course
using less energy means you need
to eat less, which leaves more time
for other things.