Nigeria, Oct. 11 -- Before a brightly colorful flower could offer nectar to a bird or a fruit could attract a mammal, plants faced a more basic problem involving what to do with the energy they captured from sunlight. This was long before humans began cultivating plants for their seeds, roots, fruits and oils. Capturing that energy was only the beginning, because a living plant also had to use some of it immediately, keep some through the coming night and move some from one part of the plant to another. Some also had to be preserved through a season or, in many cases, left behind in a seed to support a new plant that had not yet begun life on its own.

Photosynthesis makes this remarkable arrangement possible by allowing plants to use su...