For many years, Norwegian fishermen have been fishing cod from the sea. Fishing is usually done with nets that catch the large fish and allow the small ones to escape. But one day the large fish started to disappear, and this is bad for the fishing industry. Scientists try to find out what is going on. Did the fish evolve towards a smaller size, so that now they can escape from the fishermen’s nets? Are the fishermen loosing their business because of evolution?