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Biological wonder of evolution is far from random

“The human eye, or brain, or body, are marvelous and complex. To believe they could result from random mutation is like believing a tornado could sweep through an aircraft factory and put together a 747.”

True enough. But this typical anti-evolution statement has nothing to do with evolution.



The blueprints for constructing and maintaining our bodies are stored in long, parallel chains of DNA. For the information to be stored and read, the DNA chains must be disassembled. This means they can’t be held together too strongly – if they were, their information could not be read; we wouldn’t be able to carry out the processes that keep us alive.




The fact that DNA is easy to take apart means that it is also easily damaged – by chemicals, by radiation, by excessive heat. A bit of damaged DNA is a mutation – an incorrect bit of blueprint. Cancer is only the best-known (and most-feared) of a myriad of diseases that can result from mutations in our DNA. Some of these diseases may strike when we’re old, some when we’re still young.

Mutations are not all bad; if every cell, every organism were exactly like its parent(s), all life would still dwell, as single-cells, at the bottom of the sea. Mutations provide the raw material for evolution.

But mutations are random. Like the whirlwind in the Boeing plant, how could they add up into such beings as ourselves?

Mutation only provides the raw material for evolution. Charles Darwin’s accomplishment was to explain how these random events could be organized to give evolution a direction.

Gardeners who save seeds to plant the next year don’t save just any seeds. Rather, they save the seeds from the sweetest melons, the brightest flowers, the largest ears of corn. Farmers have been improving their fruits and vegetables for thousands of years through careful selection of seed.

Darwin’s great insight was that nature does the same thing. Suppose a mutation causes a childhood disease. The unfortunate victim is then less likely to reach reproductive age. Such a mutation does not get passed to future generations.

Another mutation, though, could endow its bearer with slightly sharper claws, sharper eyesight, or sharper mental abilities. These, in turn, could make the organism better able to obtain food. Better-fed, it is more likely to find a mate, and thus to leave offspring, some of which will carry the new mutation and be more likely to leave offspring themselves.

Bearing more and more offspring, their descendants will comprise an ever-larger portion of the population. The mutation will become common, and the population will have evolved.

Very small changes – in claws, or eyesight, or reasoning – would yield only very small advantages. Could these be enough to bring about evolution? Think of Las Vegas, where casinos need only a small percent advantage – a small percent of non-randomness – to rake in billions of dollars from people unclear on the concept of probability.

Soon the redbud trees will flower again, their reddish-mauve flowers very similar to the flowers of the peas in our gardens. Then they’ll set fruit: pea pods will hang from their stems. Botanists classify redbud and garden pea together, in the pea family. Both are descendants of a common ancestor that lived (and bore pea pods) some millions of years ago.

Without evolution, biology is a jumble of unrelated coincidences. Evolution, as J.B.S. Haldane put it three-quarters of a century ago, makes biology make sense.

Trained as a biologist, Alan Stahler is also an amateur astronomer. He teaches biology and geology at Bitney Springs Charter High School, and will start evening classes in astronomy and nature for adults and children at Sierra Friends Center (273-3183) in February. His science programs can be heard at noon on alternate Tuesdays on KVMR-FM (89.5).


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