Complex sentence: There is still much research to be done with Drosophila species and much controversy to be cleared but it is thought to be the possible key to uncover the human genome and has already been an invaluable tool for understanding evolution.
Split into simpler sentences: There is still much research to be done with Drosophila species and much controversy to be settled. The study of Drosophila is thought to be the possible key to uncover the human genome and has already been a valuable tool for understanding evolution.