Re: Stephen Jay Gould and Progress

Keith Henson (
Thu, 9 Jan 1997 09:20:45 -0800 (PST)

On Wed, 8 Jan 1997, Michael Lorrey wrote:

> Robin Hanson wrote:
> >
> > writes:
> > >I'm not sure about there being no "complexification drive". Brain sizes have
> > >increased markedly over time, and land animals with the intelligence of most
> > >dinosaurs probably wouldn't be viable today. Certainly there aren't any.
> >
> > Maximum brain size has been increasing, just as maximum body size has
> > been increasing. But I don't think there is any more evidence for a
> > local tendency in brains than there is in bodies.
> >
> Maximum body size has not been increasing. It is a function of several
> things, mostly average environment temperature. Animals during the
> glacial periods were much larger than their current counterparts, with
> the possible exception of man, an animal whose main asset, his brain,
> was not very valuable at that point due to the primitive technological
> base with which to work.

You might want to consider that large brains are *very* costly, in metabolic
expenses, the cost of getting those larger heads born, and the much higher
parental cost of caring for babies in a longer development cycle made
necessary by the brain size/pelvic size problem. Hominid brain size
increased by four fold during the ice ages, and evolution does not increase
the size of a costly item without it having a fully compensating advantage.
Or to put it another way, evolution found large brains in humans to be very
valuable indeed.

William Calvin extensively explores the idea in Ascent of Mind (on the web)
that brains expanded to provide more accurate throwing. I.e., humans came to
occupy a projectile hunter niche and needed the brain volume to hit things.
Up against the ice, part of the year it was hunt successfully or the whole
tribe died. Read it, Calvin provides the most organized ideas in this area I
know about.

Keith Henson