From: Keith Henson (keith@filoli.com)
Date: Tue Jan 21 1997 - 23:51:44 MST
On Tue, 21 Jan 1997, John K Clark wrote:
[snip mostly good stuff]
> Yes, if you plotted the average brain size of all animals from the
> extinction of the Dinosaurs to now you would find a modest increase, but
> there is nothing modest that happened to the human line. The brains of our
> ancestors got almost 5 times as big in just 3 million years,
Closer to 4 times in 2.5 million years, but this is a quibble.
and nothing
> even close to that has ever happened in Evolution before. This huge
> explosion in brain size started at the same moment we developed
More like several million years after. The real expansion of the brain
corresponds as near as can be correlated with the ice ages.
> bipedalism and a hand that can make complex motions. I don't believe
> this is a coincidence, and that's why I think the bipedalism question is
> so important.
It certainly was a prerequisite. I hate to summerize Calvin's work rather
than have you read it, but it seems that pre humans got along just fine as
projectile hunters using hand axes thrown discus style into groups of
animals at water holes/streams for millions of years. It was after humans
started living up near the ice that Calvin thinks this method would no
longer work--no waterholes when everything is covered with snow, and
during part of every winter it was hunt successfully or die since that was
all there was to eat (grass and animals). In such an environment, really
good projectile throwing made the difference between a line which left a
lot of descendants and one which left none. Calvin argues (very well I
think) that this is what drove the expansion of the human brain, the need
for enough neurons in parallel to hit small targets at a distance, and the
"pumping" effect on the human genotype as the ice sheets went up and
down. I can't recommend enough that you *read* Calvin's work before
arguing this topic. Keith Henson
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