Illustration of the US geneticist Jeffrey C Hall (born 1945). Hall has spent his career studying nervous system function and behaviour in fruit flies (Drosophila melanogaster). While studying courtship singing he found that the usual regular intervals of singing were altered in flies that had a mutation that disrupted daily sleep-wake cycles. Along with his colleague Michael Rosbash, Hall discovered the period gene, a rhythm-regulating gene, whose product accumulates during the night and degraded during the day. They went on to discover other rhythm-regulating genes, that were expressed throughout the body, and that responded to different stimuli, such as light. The same self-regulating biological clock has been shown to exist in other animals, including humans. Hall and Rosbash, along with Michael Young (who independently discovered the period gene), were awarded the 2017 Nobel Prize in Physiology or Medicine for their discoveries of molecular mechanisms controlling the circadian rhythm.