Today, why do you write with your right hand? The
University of Houston's College of Engineering
presents this series about the machines that make
our civilization run, and the people whose
ingenuity created them.
That question isn't really
fair, since many of you write with your left
hand. But hardly any of us write worth a fig with
our other hand. Frank Wilson's fine new
book, The Hand, analyzes every conceivable
aspect of the use of our hands - including
handedness.
The human species is the only one that exhibits
handedness, so we're well-advised to ask why. The
explanation that's gained greatest acceptance says
that handedness is related to throwing.
Wilson analyzes throwing and shows what a complex
process it is. If you don't believe that, just try
throwing an object with your non-dominant arm. The
synchronization of arm muscles and of the hand
muscles that grip and release the ball is terribly
complex.
Wilson argues that we had to evolve preprogrammed
brains to do that. It isn't that our other arm
can't throw; it's that we can't possibly think
through all the movements while we're
throwing.
Throwing is far from the only such hand action. The
seemingly simple action of chipping a stone to make
it into a tool required complex, coordinated hand
action. Anthropologists have learned to tell
whether right-handed or left-handed artisans
chipped off a given stone flake. They find
right-handedness going back well over a million
years, all the way back to our Homo Erectus
ancestors.
That might explain handedness, but why is the
right-hand most often chosen? The most likely
answer is William Calvin's Throwing Madonna
theory. It goes like this: Our hearts pump blood
out on the left. That's where the heartbeat is
loudest, so an infant is happiest when its mother
carries it on her left side. That means the active
arm must be the right one. If the mother has to
throw a stone at a lurking jackal, she has to do so
with her right hand.
No asymmetric action is a simple matter of training
one hand. As you throw with your right hand, you
execute a balancing pattern with your left.
Handedness patterns are shot through the whole
body. Next time you write, watch your non-dominant
hand. It'll stay surprisingly busy, repositioning
the paper and otherwise helping out. And that
brings us to the person whom you've met (or who you
might even be) who writes right-handed and
throws left-handed.
Such people are usually left-handers, taught as
children to be right-handed. Unless they were also
trained to throw right handed, they revert
to normal behavior when they're handed a baseball.
Violinists, right and left-handed alike, bow with
the right hand and finger with the left. Those
asymmetrical tasks are quite unrelated to
handedness and must be learned from scratch.
They're not preprogrammed, since they're not needed
for survival (except, perhaps, in Texas, where
"There's gotta be fiddle in the band.")
So throwing carries over to some tasks: writing,
playing tennis, using a fork. For tasks with no
echoes of a primitive past, our hands are
apparently blank slates to be patterned anyway we
wish.
I'm John Lienhard, at the University of Houston,
where we're interested in the way inventive minds
work.
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