In today’s New York Times, I’ve written a story about a simple but important question: where do new genes come from?

Some four billion years ago, when cellular life emerged, a typical primordial microbe likely had only a small set of genes. Today, however, genes abound. We, for example, have 20,000 genes that encode proteins. Dogs have their own set, and so do starfish and fireflies and willow trees and every other species on Earth.

Somehow, in all that time, evolution produced a lot of new genes. As I explain in my story, one way to make a new gene is to copy an old one. The two duplicates can then evolve in different directions. Duplicate each of them, and