G. Evelyn Hutchinson, one of the founders of modern ecology, wrote a book called The Ecological Theater and the Evolutionary Play (1965). This wonderful title succinctly captures a key feature of biological relationships. It suggests that ecological communities provide the stage on which the play of evolution takes place.

As an example, let’s look again at plants competing for resources. As a result of this competition, natural selection may favor plants that have more efficient uptake of nutrients or water. In the example of animals eating plants, natural selection may favor animals with greater jaw strength or more efficient extraction of nutrients in the digestive system. In turn, plants that avoid predation by synthesizing toxic compounds in their leaves may gain the upper hand. In each case, interactions between organisms lead to the evolution of particular traits.

To take another example from mammal–plant interactions: Selection for fleshy fruits improved the dispersal of apples because it increased the attractiveness of these seed-bearing structures to hungry mammals. Tiny yeasts make a meal on sugary fruits as well, in the process producing alcohol that deters potential competitors for the food. Already in prehistoric times, humans had learned to harness this physiological capability of yeasts, and for this reason the total abundance and distribution of Vitis vinifera, the wine grape, has increased dramatically through time.