text: The first recorded observations of oscillating genes come from the marches of Alexander the Great in the fourth century B.C.  At this time, one of Alexanders generals, Androsthenes, wrote that the tamarind tree would open its leaves during the day and close them at nightfall. Until 1729, the rhythms associated with oscillating genes were assumed to be "passive responses to a cyclic environment".  In 1729, Jean-Jacques dOrtous de Mairan demonstrated that the rhythms of a plant opening and closing its leaves continued even when placed somewhere where sunlight could not reach it. This was one of the first indications that there was an active element to the oscillations. In 1923, Ingeborg Beling published her paper "Über das Zeitgedächtnis der Bienen" ("On the Time Memory of Bees") which extended oscillations to animals, specifically bees In 1971, Ronald Konopka and Seymour Benzer discovered that mutations of the PERIOD gene caused changes in the circadian rhythm of flies under constant conditions. They hypothesized that the mutation of the gene was affecting the basic oscillator mechanism. Paul Hardin, Jeffrey Hall, and Michael Rosbash demonstrated that relationship by discovering that within the PERIOD gene, there was a feedback mechanism that controlled the oscillation. The mid-1990s saw an outpouring of discoveries, with CLOCK, CRY, and others being added to the growing list of oscillating genes.