Re: human brains v.s animal brains

Jane Andrews (
Fri, 6 Dec 1996 16:22:01 +0000

Brain size is normally compared using a measure called encephalisation
quotiant (EQ). This gives a value for the size of a species' brain in
relation to that expected for a mammal of that body size. The referent is
refered to as a basal mammal, (a hypothetical ancestoral incectivor I
think) but it doesn't really matter what the comparison is with so long as
it remains constant. So while humans of course have smaller brains that
elephants, we have very large brains in comparison with that which would
be expected for a mammal of our size, about four times bigger in fact.
As an aside, it's interesting to note that living humans have smaller
average cranial capacity than pleistocene amh.

There are also other consideration.
the shape of the brain may be as important as size. humans have a very
high proportion of neocortex. The question of shape is particularly
interesting when comparing modern humans and neanderthals.
Neanderthals had larger brains than modern humans, but they also differed
in shape, being more developed in the occipital region and less so in the
frontal region ( don't ask me what this signifies !).

Dolphins are often quoted as mammals with very large brains. They seem to
have large brains for many of the same reasons as primates, complex social
system, keeping track of changing resources etc. but they also do some
things with their brains that we don't. For example they use ultra sonic
ecolocation. If my memory serves me correctly bats also have quite large
brains ( maybe someone can confirm or refute this). They also have an
unusual sleep pattern. Dolphins only ever sleep on one side of their
brain at a time. This hemispheric sleep prevents REM which is thought to
perhaps play a role in sorting out information within the brain. So
maybe dolphins need large brains to manage all the unsorted stuff ?

This is all rather spurious, but is simply ment to illustrate that there
is more to intelligence than brain size and vice versa.

Jane Andrews.