Records of bioluminescence due to bacteria have existed for thousands of years. They appear in the folklore of many regions, including Scandinavia and the Indian subcontinent. Both Aristotle and Charles Darwin have described the phenomenon of the oceans glowing. Since its discovery less than 30 years ago, the enzyme luciferase and its regulatory gene, lux, have led to major advances in molecular biology, through use as a reporter gene. Luciferase was first purified by McElroy and Green in 1955. It was later discovered that there were two subunits to luciferase, called subunits α and β. The genes encoding these enzymes, luxA and luxB, respectively, were first isolated in the lux operon of Aliivibrio fisheri.