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

Lloyd Jacobs (
18 Aug 1995 04:31:23 GMT


Stuff snipped to here
: I have lots of loose speculation about mechanisms for increased brain
: size, (though I'm not sure how close the relationship is between actual
: cortex volume and computational ability), relating to complex
: social behaviour, as you mentioned, as well as a need for lots of
: fine motor skills in manipulation of the newly freed forelimbs,
: which I believe would have been used to launch stone projectiles
: maybe millions of years before we got in the habit of modifying them.

: ..Excuse me while I indulge in some of that loose speculation...
: I guess that what I see as prerequisites for development of our
: sort of intelligence are a complex social environment, to encourage
: some abstract conceptualization and communication, plus a
: need for lots of motor cortex to drive complex movement, thus
: increasing the amount of spare neocortex lying around loose
: to provide a home for the abstractions to ferment into a
: coherent world model. But none of this requires a savanna to
: work. Of course, it doesn't explain why lots of other social
: mammals didn't develop large brains, and substantial intelligence,
: either. Let's see... social carnivores, like lions and wolves,
: are so physically well suited to their niche that they wouldn't
: require the excess baggage. Most of the other mammals large
: enough to pack a big brain are either solitary, or ruminants
: with pretty simple social systems, and no need for fine motor control.
: The only exceptions that immediately occur to me are other
: primates, and elephants. As big brains seem to be so useful,
: it's odd that they wouldn't show up more often, least in these
: candidates.

The short answer is: They don't have large brains because they are not
smart and thus don't need one.

What do you think of the possibility that the bulk of our brain is
redundant for the purpose of durability? In the days before writing
surely it was necessary for durable intellects to provide cultural
continuity and off hand, I can't see any other mechanism to repair the
brain other than having pre-existing, redundant, spare, extra neurons.
You could try regenerating tissue but nah, you have problems with
controlling the regeneration so that it doesn't destroy intact dendritic
pathways. And then what good is it since the valuable memories in the
damaged tissue are already lost for good.

Collateral regeneration is the way.

Also, I have heard of people (who were in their teens) with the congenital
disease hydrocephalus having only about 15 percent brain of normal
brain mass while having 100 percent normal mental function.

I'm starting to believe that there were pretty clever small-brained
apes running around about 4 mya but didn't really take advantage of that
general intelligence until they evolved with greater longevity and that
required a larger, tougher brain. As well as for longevity, a tougher
brain would also be useful in maintaining good function in case of
disease, famine and trauma.

What do you think?


There's a Fundamentalist reborn every minute!