In today’s Washington Post, writers Rick Weiss and David Brown offer a succinct, readable explanation of how natural selection works:
By some accident of nature whose workings neither man [Darwin and Wallace] could explain, an organism may exhibit a variation in shape, color or body function new to the species.
Although most of these new traits are damaging — probably lethal — a small fraction actually help. They may make it easier to hide from predators (like a moth’s coloration), exploit a food source (an anteater’s long tongue), or make seeds more durable (the coconut’s buoyant husk).
If the trait does help an organism survive, that individual will be more likely to reproduce. Its offspring will then inherit the change.
They, in turn, will have an advantage over organisms that are identical except for that one beneficial change. Over time, the descendants that inherited what might be termed the “happy accident” will outnumber the descendants of its less fit, but initially far more numerous, brethren.
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What is hard to understand about this process is that it is essentially passive. The mechanism is called “natural selection” because the conditions at hand — nature — determine which accidents are beneficial and which are not. Organisms do not seek ends.
Giraffes do not decide to grow long necks to browse the high branches above the competition. But a four-legged mammal on the savannah once upon a time was endowed with a longer neck than its brothers and sisters. It ate better. We call its descendants giraffes.
(Emphasis and extra paragraphing added.)
Weiss and Brown also report on recent developments that “put the very theory of evolution to some tough new tests.”
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