Field mustard is an annual plant that grows wild in many regions of the world. It has small yellow flowers and is pollinated by insects. Field mustard has to flower and produce seeds to give rise to the next generation. Southern California experienced a severe drought between 2000 and 2004. Plants that flowered earlier reproduced. Those that flowered later died without producing seeds. This led to more early-flowering field mustard plants. This change in population characteristics took only a few generations. How do you think scientists discovered that the flowering time of the field mustard had changed?