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Summary: In making his case for the role of natural selection in
evolution, Darwin started by pointing to the enormous
phenotypic variation that could be achieved in just a few
generations of artificial selection. In Darwin's day, the
importance of good breeding practices in determining the
productivity and quality of a farmer's stock or the crop
size of a pigeon fancier's prize bird was clear to all, and
Darwin's artificial selection arguments provided a power-
ful foundation for his idea that competition for limited
resources could similarly tailor phenotypes, and ultimately
create new species, by selecting for beneficial traits.
Today, we can use artificial selection to breed not just
organisms, but also the protein products of individual
genes. By subjecting them to repeated rounds of mutation
and selection (a process usually referred to as "directed
evolution"), we can enhance or alter specific traits and
even force a protein to acquire traits not apparent in the
parental molecule. And, just as in Darwin's day, these arti-
ficial selection experiments have the potential to teach us
a great deal about evolution, only now at the molecular
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