IS A SIMPLE PROCESS
May 23, 2010
one candidate in the Alabama Republican gubernatorial primary race accused
another candidate of being in favor of teaching evolution in schools,
as if that were a political spear through the heart. One newspaper article
suggested that the political shield held up to deflect that spear was
an assertion that the accusation is untrue. A spokesperson in the shield
holder's office told me that the candidate considers "evolution to
be the most dominant theory to explain the origin of life." Not,
perhaps, a ringing endorsement of the need to teach evolution in school;
better, however, than what some politicians are saying.
But as much
fun as dissecting Alabama politics might be, this column is an attempt
to explain to certain people (such as the spear thrower) what "evolution"
means. The following is written for the nonbelievers.
in its simplest form explains how the natural world works through natural
selection. The consequences of evolution are seen every day. Charles Darwin's
ideas of natural selection, survival of the fittest, and evolution are
elegant in their simplicity. Anyone interested in understanding the way
the world works should consider the basic concepts of the process. The
following example shows how evolution (change) in a lizard species could
occur in a natural manner.
selection operates because some individuals have a trait that makes them
more likely to survive than others. In this example, a species of yellow
lizards lives on an island. Their yellow body color is genetic, but a
few individuals have genes that produce green individuals. Lizards that
are dull green in color are rare, but they are the same species as the
yellow lizards and interbreed with them. The lizards live peacefully in
their tropical paradise until a type of lizard-eating hawk moves onto
over the thick, dark green vegetation of the island, hawks easily discern
bright yellow lizards. If a green lizard and a yellow one are sitting
side by side on a green bush when a hungry hawk flies overhead, the yellow
lizard will stand out like a beacon. The green lizard will probably escape
detection. Which lizard is more likely to become hawk fodder? Obviously,
the yellow one.
the green genes are more likely to be the ones passed on to the next generation.
As the natural process in which hawks select and remove the yellow lizards
continues, proportionately more green genes are inherited than are yellow
ones. Eventually, the hawks virtually eliminate the yellow lizards while
green lizards become abundant. Thus, the island lizards have evolved--changed--to
become a population of green lizards, with yellow ones being very rare.
Basic evolution has prevailed.
example, which most pet owners are aware of, concerns flea collars. Anyone
old enough to remember the advent of flea collars in the 1960s will tell
you that they were a godsend for flea-ridden dogs and cats. You put the
collar on the pet and the fleas were gone within days, if not hours. No
fleas all summer or the rest of the year. But flea collars are no longer
as prevalent as when they were introduced, and the explanation is a simple
one: the fleas evolved.
insecticides in the collars that killed the fleas and did not harm the
dog or cat were very effective, killing probably 99.9 percent of the fleas.
But guess what. That means 0.1 percent of the fleas did not die. They
were able to survive the chemical onslaught and produce offspring. Those
offspring were genetically different, although only slightly so, from
the fleas that were dying in droves. The survivors had genes that allowed
them to tolerate the insecticides, and they passed those genes on to their
in genetic makeup within a population or a species is the essence of evolutionary
change. So, for example, whatever flea protection you are using now will
probably be less effective in 10 years for the same reason flea collars
are now obsolete: evolution.
a simple concept even a schoolchild can understand it.
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