Robert Pringle and Paul Ehrlich have an editorial in the Sacramento Bee about Senator Sam Brownback's evolution stance. In response to Senator Brownback's assertion that no one has ever witnessed speciation, they have an interesting analogy:

Brownback's argument rests on the fact that no person has ever seen a species produced by a gradual process. Then again, no person has ever seen a giant redwood tree grow from a seed. But one can find redwood trees of all sizes and observe their incremental growth within years.

Good point.