brains, Tools & Canines

Wed, 22 Feb 1995 10:58:13 -0500

I have tried to resist entering this discussions, but I failed.
Two ideas for the evolution of intelligence have been debated -- technology and
social life -- as though they were the only ones worth considering. There are
others and many are presently (and permanently?) irresolvable.

To suggest two, consider (1) foraging efficiency and (2) overcoming limitations.

The first has been argued by several people. Primates and other animals need to
map resources in time and space. A species that is better able to locate
resources with minimal energy expenditure has obvious advantages. Selection for
foraging efficiency would become more important if the animal operated over a
larger range, exploited mostly seasonal resources, or had higher energy needs.
Great apes and presumably the human ancestor meet these requirements. All need
some higher levels of dietary supply since they have larger brains, but mostly
because they are large animals living on relatively rich and sparse diets of
fruit. (Gorillas are an obvious exception, but probably their ancestors ate

How do we decide among these? I don't know.
In tool, social, and foraging models we face the problem of why other species do
not have big brains. After all, chimps make and use tools, have complex
societies, and face similar foraging problems. Perhaps there is a threshold
effect -- once brains reach a certain size, positive feedback takes over and
increase proceeds exponentially. Thus hominids were under greater selection for
intelligence than chimps because they had to get along with a society of smarter
competitors or because they found even new possibilities for their tools or
because larger brains demanded even more foraging efficiency.

A different approach assumes that bigger brains or smarter ones are always
advantageous for many reasons at once. The reason some animals are smarter than
others is because they overcame one or more constraints on brain size. The
obvious constraints are metabolic: supplying the brain with energy, keeping it
cool, growing it in the fetus, etc. Humans simply overcame more constraints than
did other species -- perhaps by incorporating more meat in the diet. See Martin
or Falk for development of these ideas. Did intelligence drive metabolic support
systems or visa versa?

These are not answers to the discussion. I just see your debate stuck in a rut
at a rather simplistic level. I don't believe that any one selective pressure is
going to explain the evolution of human intelligence.

By the way, canines were reduced so that australopithecines could grind their
food from side to side. This is consistent with changes in the arcade shape,
enamel thickness (now that ramidus is said to have thin enamel again), molar
enlargement, molarization of premolars and sometimes canines, and hypertrophy of
chewing muscles.