The Shape of Things to Come. What causes the origin of species? Darwin believed it was the gradual accumulation of tiny mutations. The fossil record, however, shows something completely different-the sudden emergence of whole new species with no apparent ancestors. By studying the genes that control whether an organism develops into a fruit fly or a mouse, a new branch of science is trying to answer evolution's biggest puzzle. Peter Evans reports. Producer Paul Arnold. E-MAIL: scirad@bbc.co.uk