What distinguishes food crops from other plants has nothing to do with taste, nutrition, or whether they contain poisons. The plants we eat are atypical because of their particularly dull sex lives.

Many biologists believe that the reason there are so many species of flowering plants is that each has become dependent on a unique species of insects that coevolved to pollinate it. In other words, these are plants with elaborate sex lives. The more unusual the mechanism of insect pollination, the greater the genetic separation among plant populations becomes, almost as if they had evolved on different islands.

This explains why there are roughly 25,000 orchid species. Orchids are the kinky exhibitionists of the botanical world. Many of them have extremely elaborate flowers that have evolved to trick male bees or wasps into trying to copulate with them, thereby ensuring that they are regularly pollinated.

This explains why we don't farm orchids for food. Seducing bees and wasps might work well for a few individual flowers, but it would never work on an agricultural scale. There would never be enough male wasps to pollinate an entire crop; and if there were, they would soon tire or wise up.

Most food crops, by contrast, can be pollinated by different types of insects. They can be successfully cultivated around the world, using whatever insects are available to pollinate them. The most common crops of all - wheat, maize, and rice - are grasses that rely on the wind for pollination.

A more adventurous plant diet is possible. But it would have to accommodate the quirky sex lives of what we include in it.

The author is professor of botany at Aberystwyth University and author of The Nature of Crops.

Project Syndicate