Language did not evolve only in the distant past. Our shared understanding of the meanings of words is ever-changing, and we make conscious, rational decisions about which words to use and what to mean by them every day. Applying Charles Darwin's theory of "unconscious artificial selection" to the evolution of linguistic conventions, Daniel Cloud suggests a new, evolutionary explanation for the rich, complex, and continually reinvented meanings of our words.

The choice of which words to use and in which sense to use them is both a "selection event" and an intentional decision, making...