Today, we learn a lesson from a shark's tail. 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.
The shark is such a powerful
symbol of menace! Zoologists tell us he's a
primitive fish. The shark has been around for a
hundred million years. We look at him and see
eerie, primordial forces of evil. We're so caught
in the symbolic power of the beast, we have trouble
seeing him for what he is.
His tail, for example: It's all wrong. Most fish
have symmetric tails. But the shark's tail is
unique among fishes. It's long on the top and short
on the bottom. Doesn't the swimming force act
downward? Doesn't it drive him down into the water?
Worse yet, the shark is heavier than water. Don't
his pectoral fins constantly have to push him
upward as he moves?
We conclude that the shark suffers extra drag
forces -- that he's inefficient unless he's diving.
We've believed that for years. The development of
this primitive fish seems to have been arrested,
before it was finished.
Yet he's been with us too long. He's survived when
other species have not. So zoologist Keith Thomson
grew curious. He asked a diver to follow a shark
with a camera in the New England Aquarium. The
diver gave him a set of photos that showed the
precise motion of the shark's tail.
He does far more than swish his tail back and
forth. He controls the upper tip with the grace of
a seagull. He changes the direction of the thrust
by tilting the tip, just so.
There's more. We find we've missed a simple point
of me chanics as well. Think about the last time
you used a screwdriver on a stuck screw. The longer
the handle of the screwdriver, the better you did
with it. That's because you can tilt it off the
axis of the screw, without slipping out of the
slot. That gives you a lot of extra leverage.
The shark's seemingly crazy tail is like that. It
gives him an extra grip when he has to turn
suddenly. He's not only fast, he's maneuverable as
well. He is a formidable foe.
So we look further and find still more. His brain
is large. His sense of smell is highly developed.
The shark, like the cockroach, is ancient. He
survives for good reason. In the end, we have to
acknowledge a superb piece of design, after all.
We've said before in this series that good design
is timeless. You don't try to improve upon the
wheel or the violin. So it is with the shark. And
that is why he's lasted -- ever since life on Earth
was young.
I'm John Lienhard at the University of Houston,
where we're interested in the way inventive minds
work.
(Theme music)
