At the beginning of the experiment, none of the flies would eat food with any amount of cadmium. However, in cages with high competition, some flies began to switch to the toxic food, and passed this characteristic to their offspring. The rate of evolution into niches was fastest in the cages with the highest competition, said Bolnick. Bolnick did not observe the formation of actual new species in the experiment. Biologists think that separation into niches that tend not to interbreed marks the beginning of the process.
Biologists have two basic models for how new species form.
In one model, a group of individuals is physically isolated from the rest of the species, for example by a mountain range. These ideas on competition and species formation were first put forward in the 1970s, but new theories developed in the last five years have made it possible to test them, said Wainwright.