Жан Жак д’Орту де Мерен: Геофизик, астроном и пионер хронобиологии XVIII века

18th century French geophysicist, astronomer, and chronobiologist

Jean Jacques d'Ortous de Mairan (26 November 1678 – 20 February 1771) was a French natural philosopher (physicist), born in the town of Béziers on 26 November 1678. Over the course of his life, de Mairan was elected into numerous scientific societies and made key discoveries in a variety of fields including ancient texts and astronomy. His observations and experiments also inspired the beginning of what is now known as the study of biological circadian rhythms. At the age of 92, de Mairan died of pneumonia in Paris on 20 February 1771.

De Mairan attended college in Toulouse from 1694–1697 with a focus on ancient Greek. In 1729, de Mairan constructed an experiment showing the existence of a circadian rhythm in plants, presumably originating from an endogenous clock (See 'Experiment on circadian rhythms in plants' below). In 1731, he also observed a nebulosity around a star near the Orion nebula. This was later designated M43 by Charles Messier. In 1731, he published "Traite Physique et Historique De l'Aurore Boreale" (a short summary appeared in the Philosophical Transactions) in which he put up a novel hypothesis that the Northern Lights are caused by the Sun, as the interaction of the atmosphere with the zodiacal light. At the time, the aurorae were thought to be 'flames' caused by sulfurous effluvia emanating from the Earth.

In 1729, de Mairan performed an experiment that demonstrated the existence of circadian rhythms in plants, specifically the Mimosa pudica. He was intrigued by the daily opening and closing of the heliotrope plant and performed a simple experiment where he exposed the plants to constant darkness and recorded the behaviour. These results may have gone unnoticed had his colleague, Jean Marchant, not published them for de Mairan. Alternatively, it may be that de Mairan simply was not available to present this work himself. It was quite common at the time, when travels were slow, for one scientist to present the work of another. Whatever the case, this rather obscure one page contribution by a prolific and highly respected academician did stand the test of time. It is by far the most if not the only paper by de Mairan which is still quoted in the current scientific literature (bar purely historical reviews). When describing his work with eclosion rhythms in his Drosophila models or the rhythmic running activity of mice, founder of modern chronobiology, Colin Pittendrigh, recognised the work of Jean Jacques d'Ortous de Mairan. A video showing circadian rhythms in a cucumber plant in constant conditions, similar to what de Mairan observed, can be seen .

Despite Marchant's publication of de Mairan's work, which might have suggested the existence of endogenous biological clocks, rhythms in plant movements were for a long time thought to be extrinsically controlled, by light and dark cycles, or magnetic and temperature oscillations, or even a mysterious, yet to be identified X factor. In 1823, almost a century after de Mairan's work, the Swiss botanist Augustin Pyramus de Candolle expanded on it by measuring the free running period of Mimosa pudica leaf movements in constant conditions, finding them to be 22–23 hours long. This was probably the first hint of what is now called the circadian (from Latin circa, about, and diem) nature of such endogenous rhythms, found in practically all living organisms, including some bacteria.