GIRAFFE STORY SHOWS WHY SCIENCE STICKS ITS NECK OUT
BYLINE: Steve Rissing, For The Dispatch
It profits some to argue that science and religion
are equally dogmatic
and thus should be taught equally in science classes. But naturalism
doesn't equate to theism; to argue otherwise denigrates both equally
and
fails to acknowledge the power of these uniquely human insights.
Science builds on its mistakes and misunderstandings
and becomes
stronger. Few, if any, religions spend much effort asking, "Where might
we
be wrong?''
Science does precisely this, however.
A good example is the giraffe's
long neck, a favorite topic for Noah's ark cartoonists and an icon
of
Darwinian natural selection in science texts.
The normal story begins with an early Franch biologist,
Jean-Baptiste
Lamarck. He suggested that animals passed to their offspring
characteristics they acquired during their lives; his favorite example
was
shorebirds stretching their legs to avoid getting wet. He recognized
evolution, but his mechanism had problems: How did changes from stretched
legs get into gametes (reproductive cells) to benefit the next generation?
Darwinian natural selection provided a more reasonable
alternative
hypothesis and is standard fare in biology texts: Giraffes with random
mutations for slightly longer necks could eat leaves unreachable by
others.
They therefore survived and reproduced better than their competitors
did.
Lamarck, however, mentioned giraffes only in a postscript,
and Darwin
mentioned them only for their "fly swatter'' tails until the last edition
of his Origins book, doing so in response to an anti- evolutionist
named
St. George Mivart.
This 19th-century British biologist had criticized
Darwinian natural
selection by raising the "giraffe problem'': Neck-lengthening requires
many
anatomical changes, so how could such changes occur simultaneously?
The
same argument is advanced by today's proponents of the "intelligent
design'' theory of creationism.
Darwin expanded Origins to explain how complex changes
could occur
through random mutation and selection. He even admitted that Lamarck's
theory might play a role, but he argued that natural selection was
more
important.
In 1996, neo-Darwinian (and gadfly) Stephen Jay Gould
recalled the
controversy in a commentary in Natural History. He suggested that neither
natural selection nor Lamarckian ideas did much to explain giraffe
necks
and data from the African veldt soon supported him.
Researchers watched giraffes in the field, especially
during droughts.
The animals, especially females, ate leaves with their necks horizontal
or
bent. Males, however, clobbered each other with their necks and armored
heads during mating season; sometimes, the loser died.
This isn't Lamarckian inheritance of acquired traits
or even natural
selection. It's a force of evolution Darwin called sexual selection:
the
same force that gives us brilliantly colored male peacocks, cardinals
and
bluebirds and human males who are generally stronger and larger than
females (but who usually die earlier).
So, is Darwinism as dead as a puny male giraffe in
a bolo-neck contest?
No, natural selection isn't as good an explanation as sexual selection
for
this textbook example, and the texts need to be updated. That's OK;
that's
science; that's how we learn.
A sexual selection counter-example to natural selection
doesn't
disprove evolution; after all, Darwin described both. It profits us
not to
ignore such insights into our existence and that of others with whom
we
share this planet.
Steve Rissing is a professor in the Department of
Evolution, Ecology
and Organismal Biology at Ohio State University and director of the
university's Introductory Biology Program.
POWRÓT