We’ve been tinkering with the DNA of other species for thousands of years. We just didn’t know what we were doing.

Starting about ten thousand years ago, humans began to steer the evolution of animals and plants. Our ancestors collected certain seeds instead of others, started to plant them in gardens, and gradually produced domesticated crops. They didn’t know which genetic variants they were choosing, or how those genes helped build new kinds of plants. All they knew was that some plants were better than others. Over thousands of years, for example, an innocuous bush called teosinte turned into tall stalks with gargantuan seeds–otherwise known as corn.

Our ancestors could see the outward changes they were bringing to crops like corn, as