A species of fly lays its eggs on the fruit of hawthorn trees, where the larvae develop. About 150 years ago some flies began laying eggs on the fruit of apple trees instead. Apple and hawthorn trees grow side by side in the same area. The flies mate on or near the fruit they grew up on, and apple fruit ripens a few weeks earlier than hawthorn fruit. Two "races" of the fly now exist, one on each type of fruit.
Define sympatric speciation.
[2]
Explain how reproductive isolation can occur between the apple and hawthorn races even though they live in the same area.
[3]
Suggest how biologists could find out whether the two races have become separate species.
[2]