Essay 14  08/12/05  Physical Anthropology, Neuroscience, Optimal Foraging Theory
Foraging Demands and Brain Expansion
Since 1859, the year that Charles Darwin published his work On the Origin of Species,
scientists have known that the differences between humans and other animals are due to
historical differences- each animal species evolved in different environments, and because of
this, acquired different traits.  This fact has led theorists to speculate about the origins of human
intelligence.  At first anthropologists were at a loss, they could not explain the proportionately
large size of the human brain in terms of historical differences between humans and apes.  
Now, insightful theories seem to agree with anthropological data and common sense- and
most scientists feel somewhat satisfied with the current explanations.  It seems that the most
important historical difference that allowed the expansion of the human brain, was a profound
change in our species’ ecological niche (place on the food chain).

The brain, and the nervous system in general, consume a large percentage of the food that they
enable animals to seek out and obtain.  In fact nervous (brain) tissue burns more than 20 times
the amount of calories that skeletal muscle does at a resting rate.  Because nervous tissue
consumes such large amounts of energy, most animals cannot afford to develop big brains-
their place on the food chain simply cannot support such an expensive organ.  Chimps and
other apes have a lifestyle that demands intelligence, more so than that of their smaller cousins,
the monkeys, and this accounts for why apes have larger brains than monkeys.  

Chimpanzees, the animals species that we are most closely related to, inhabit an ecological
niche that makes high demands on intelligence and a capacity for insight.  Like most animals,
young chimps must learn, and later employ, certain skills in order to obtain enough food to
survive.  Unlike other animals though, chimps have a prolonged learning period- their mother’s
often teach them to forage, one on one, for over a decade.  A large, energy expensive brain is
necessary for young chimps to acquire the necessary skills, and to refine their foraging

Geological evidence shows that around 6 million years ago the thick forests that were home to
many species of apes began to thin out, forcing some of the apes to lumber around on the
ground in search of food.  Around 4 million years ago our ancestor, Australopithecus, first
began to walk upright on two feet.  The fossil skeletons that we have found of
Australopithecines (which include the famous Lucy) have shown us that they would have stood
a little over 3 feet tall and had a brain no bigger than a chimpanzee.  This was a tremendous
surprise to primatologists at the time because it meant that bipedal walking did not necessitate
a big brain.  It is now thought that the ability to walk on two feet allowed access to a vastly
different ecology, and that this change influenced the brain to expand to its present size.  

Today we can see that the lifestyle of modern hunter-gatherers requires incredible intelligence.  
From an early age forager peoples are forced to learn the skills and methods of survival.  
Whereas most chimps can learn to be self sufficient within the first decade of life, most hunter-
gatherer humans do not reach peak productivity until their mid-thirties.  This is where our
energy expensive brain allowed us an advantage, it helped us to acquire, store and utilize the
important lessons that we learned from our parents, and family.  It allowed the creation of tools
which in turn enabled us to catch large game and extract difficult-to-procure vegetative matter
and other calorie dense foods to support our energetic lifestyle.

In the last few decades, theorists have pointed out other factors that probably contributed to the
large brains seen in our species.  It is now thought that social intelligence and an aptitude for
language and abstract thought allowed the bigger brained humans to produce more offspring
than the smaller brained humans, thus increasing the average brain size for our species.  
However, it still seems that the primary factor responsible for the cognitive differences between
an ape in the zoo and your average working class human is the place on the food chain that
was filled by their respective ancestors.
Organization for the Advancement of   
Interdisciplinary Learning