Re: Brain size (was Re: AAT QUESTIONS...)

Lloyd Jacobs (
19 Aug 1995 17:09:51 GMT


: I suppose you mean `tougher' in a metaphorical sense, ie. more
: resilient. ...Age is definitely a key to the development of culture.
: It would be hard to retain a knowledge pool if people kept
: popping off at age 25 or so. But if brain size doesn't directly
: correlate to intelligence, what does determine it? Some change
: in the nature of synapse development? I'm not sure that our
: brains develop any differently than other mammals, they're
: just bigger. And even short lived mammals show (to some extent)
: a correlation between the size of specific areas of the cortex
: and the degree of facility they display in the functions that
: correspond to those areas. For just one example, consider the
: olfactory processing regions of the canine brain.

That's it exactly (although I'm not just referring to normal longevity).

The dog's olfactory area might be larger because it depends on it for a
living. It not only adds longevity to that particular faculty but also
protects it in case of a severe illness, famine or anything else that may
cause damage to it. But that region I believe is already fundamentally
more complex than our own olfactory area given equal units of tissue.

Here's a list of factors that may determine relative size in a
particular region:

1 Dependence on it for survival
2 Longevity of the species
3 Harshness of the environment
4 Ability of the species to fight off disease, famine etc.
5 Preservation of learned behavior over time
6 Complexity of the particular function

Obviously you can't have a single cell performing a useful function so
here size or number is important and I added complexity at the end. The
critical minimum of cells probably varies depending on its function but I
feel it is relatively small.

If improving intelligence in a species were as simple as adding a bunch
of cells than I think we would have seen, as you suggested, a lot more
big brained beasts like ourselves. Humans had to evolve the talents
involved in intelligence first (which resulted in a slightly larger brain)
and from there adding the bulk of cells was merely the insurance and a
reflection of our dependence on it.