HE MAY BE one of the country’s best known and most accessible explainers of science, but Bill Nye, a former mechanical engineer, got his showbiz start in comedy. A role he played on a local Seattle sketch-comedy TV show eventually evolved into the gag-laden syndicated program for which he’s best known: “Bill Nye the Science Guy.” Although the show wrapped in 1998, after 100 episodes, Mr. Nye retains the moniker, as well as his mission to explain at times complex scientific principles in plain English. His latest book, “Undeniable,” unpacks evolution—which he believes to be “the fundamental idea in all of life science.”

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