Gabriel Rogel Cuevas
Professor Potter
ANTH – 1020 - 004
Bipedalism vs. Large Brain
One of the things that makes our species unique are the two traits the separates humans
from other primates, bipedalism and a large brain. These characteristics are a direct result of our
ancestors being able to adapt to their habitats. “Evolution is an opportunistic process - species
change over time, but only some of these changes prove to be advantageous to an organism's
survival.” (Costandi, 2012) These characteristics set us apart, but what came first walking upright,
or the development of a large brain.
What is bipedalism? Bipedalism is referring to the locomotion of two legs this can include
anything from walking, jogging, and running. While the transition to walking upright from walking
on all fours, and the development of our brain did not happen overnight. There was some major
physical changes along the way that helped in the development of both traits. For many years the
scientific community belief that the increase brain size was what led to bipedalism. Many of the
early discover hominin fossils were bipedal and all had large brains like modern human which led
to this belief. This all begin to change with the discovery of two new hominin fossils.
In 1924, Raymond Dart found the first australopithecine, known today as the Taung Child
in South Africa. This specimen belonged to the species Australopithecus Africanus and had
relatively a small brain similar to that of modern chimpanzees. The Taung Child dates back
between 3-1 Mya. The second discovery came in 1974, Donald Johanson found the nearly
complete fossilized skeleton of Lucy, a member of the species Australopithecus Afarensis dating
to 3.2 Ma. Lucy was unique at that time, because she showed both a small brain, similar to that of
modern chimpanzees, and the features characteristic of bipedalism, similar to that of humans.
The physical changes in evolution the led to bipedalism occur from 6 – 2 Mya. Some of
the characteristics that begin to separate early hominins from other primates are the pelvis, legs,
feet, and the foramen magnum. These characteristics led to certain advantages for our early
hominin ancestors. They were able to free their hands to carry food and their young, cover longer
distances, and to survey their surroundings efficiently.
Around 6 Mya the first change began to take place the upper thigh bone formed a bridge
with the pelvis to support the weight of the body better. (Lovejoy, 2005) Orrorin Tugenensis dates
back to about 6 Mya suggesting that they may had been one of the earliest to have walked upright.
Another trait that begin to develop around 4 Mya is the wide area below the knee joint which
allowed early hominids to balance on one leg when taking a step. (Lovejoy, 2005) By this time
early hominins were mostly bipedal. A good example of this is Australopithecus Anamensis who
dates back between 4.2 – 3.9 Mya. Around 2.5 Mya the back begin to curve which is a uniquely
human trait the curvature allows for the shock and absorption of stress put on the lower back by
the bipedal locomotion. (Lovejoy, 2005) This trait can be traced to Australopithecus Africanus
which dates back to 3 – 1 Mya. By 1.9 Mya early hominins were fully bipedal, but they still need
traits like broader hip bones and the long thigh bone to develop to be completely as humans.
(Marchal, 2000)This traits date back to the same time period 1.9 Mya, an example of this is Homo
Erectus who possess all traits and were fully bipedal.
As early hominins became more mobile and begin to explore new habitats and experience
new climates. Natural selection begin to show itself when this early hominins begin to show signs
of bipedalism, get bigger bodies, evolved larger more complex brains. The latter became crucial
to the survival of early hominins. Large more complex brains allowed hominins to process and
store a lot more information. This was a big advantage in adapting to new habitats and developing
social interactions. During human evolution the brain size has tripled. The human brain is the
largest and most complex of any primate.
The human brain has many advantages like the storing of large amounts of data, solve
problems, and create abstract ideas, and images. Large brains also come at a cost for example a
large brain requires more energy, it requires 20% of oxygen supply and blood flow while making
childbirth more difficult and painful for women. The latter is also known as the obstetric dilemma
and played a major role in the development of fontanelles in the skull to ease the head thru the
birth canal during labor. (Costandi, 2012) Like bipedalism these changes did not happen overnight
but resulted as an evolutionary response to physical, environmental, and climatological changes
the resulted in the genealogical and physical changes we see today in humans.
The first changes in brain size happen between 6 – 2 Mya, these changes were minimal.
Orrorin Tugenensis who is a contemporary of this time early time period had the brain size of a
modern chimpanzee between 275 and 500 cm³. (Schachner, 2013) As early hominins became more
mobile and began to explore areas outside of Africa, the challenges they faced along with an
increased in body size led to an increase of brain size as well from 2 Mya to 800,000 ya. For
example Homo Erectus who lived in the same time period and was fully bipedal had and average
brain size of 900 cm³. Homo erectus also use their more complex brain to develop new
technologies for example their tool making when from using olduwan tools to acheulan tools as
their brain develop. The greatest and fastest growth period of the human brain occurred between
800,000 and 200,000 years ago. Heidelbergensis would be an example of this time period their
average brain size was 1250 cm³. During this period dramatic climate changes made their
environments unpredictable and a larger more complex brain led to new and different ways to
interact in their new surroundings. A more complex brain helped Heidelbergensis develop and use
new technologies such as the exploiting of marine resources, use and control of fire, and new
acheulian tools.
The evolution of bipedalism and the brain were independent of each other in the evolution
of humans. The changes that occurred because of the evolution in bipedalism may have led to the
increase of the brain size unintentionally. According to an article in the website The Guardian.com
“The new findings suggest that further brain expansion, as well as reorganization of the prefrontal
cortex, could have occurred as an indirect result of the pelvic modifications that followed the
transition to bipedalism.” (Costandi, 2012) As the research continues to show it might not have
bipedalism vs. large brains, but instead bipedalism and large brains working, and supporting one
another all long.
Works Cited
Costandi, M. (2012, May 7). science/neurophilosophy. Retrieved from The Guardian:
http://www.theguardian.com/science/neurophilosophy/2012/may/07/1
Lovejoy CO. 2005. The natural history of human gait and posture. Part 1. Spine and Pelvis. Gait
& Posture 21(1):95-112.
Lovejoy CO. 2005. The natural history of human gait and posture. Part 2. Hip and Thigh. Gait &
Posture 21(1):113-124.
Lovejoy CO. 2007. The natural history of human gait and posture. Part 3. The Knee. Gait &
Posture 25(3):325-341.
Marchal F (2000) A new morphometric analysis of the hominid pelvic bone. Journal of Human
Evolution 38:347-365.
http://gmex714801.weebly.com/