Evolution Predicts the Flowering of Mustard Plants

Here’s another prediction: under prolonged drought, natural selection will lead to the evolution of plants that flower earlier than their ancestors. This is because, during a drought, soils dry out quickly after the rains. If you’re a plant that doesn’t flower and produce seeds quickly in a drought, you leave no descendants. Under normal weather conditions, on the other hand, it pays to delay flowering so that you can grow larger and produce even more seeds.

This prediction was tested in a natural experiment involving the wild mustard plant (Brassica rapa), introduced to California about 300 years ago. Beginning in 2000, Southern California suffered a severe five-year drought. Arthur Weis and his colleagues at the University of California measured the flowering time of mustards at the beginning and end of this period. Sure enough, natural selection had changed flowering time in precisely the predicted way: after the drought, plants began to flower a week earlier than their ancestors did.

Scientists predict how a drought will affect the flowering time of plants in California, and it comes true.