Magazine article Times Higher Education

Cometh the Hour, Sleepeth the Man

Magazine article Times Higher Education

Cometh the Hour, Sleepeth the Man

Article excerpt

Daily variations in human activity are driven by our built-in biological clocks, finds Greg Murray.

Internal Time: Chronotypes, Social Jet Lag, and Why You're So Tired

By Till Roenneberg

Harvard University Press 288pp, Pounds 19.95

ISBN 9780674065857

Published 26 April 2012

Imagine driving through the centre of a large city at 4pm. Now imagine the same trip, but at 4am. The difference between peak-hour slog and pre-dawn jaunt exemplifies the daily variation in human behaviour - late afternoon we're up and about fighting for space on the roads, while in the early morning most of us are in bed.

This observation becomes interesting when we realise that dramatic 24-hour rhythms in activity are not simply a reaction to environmental conditions or social norms, but are driven endogenously (from within) by a self- sustaining biological clock. Humans share this clock (the "circadian system") with almost all other living things. The clock is adapted to prepare the organism for daily changes between light and dark, and is known to control a huge range of physiological and behavioural functions. Till Roenneberg's book is an engaging and informative layman's introduction to circadian science and its implications for contemporary humans.

In 24 chapters (get it?) Roenneberg uses the strategy of problem-based learning to introduce the reader to all major features of the circadian system. Each chapter commences with a brief vignette demonstrating an aspect of clock function/dysfunction. With the possible exception of one murder-mystery narrative, these vignettes work well as set-ups for information about the interaction between internal time, social time and sun time.

The first argument to prove is that ubiquitous 24-hour rhythms in physiology and behaviour are in fact driven by the clock. The notion is introduced with an anecdote about the 18th-century French astronomer Jean- Jacques d'Ortous de Mairan, who found that his mimosa plant maintained its daily rhythms in a light-proof box. In a humanising twist, we hear that de Mairan's excitement about this discovery triggered one of his frequent episodes of insomnia. Later, we hear about a family of late 20th-century laboratory hamsters with unusually fast body clocks, and how interbreeding and transplantation confirmed that their behavioural rhythms were caused by the clock. …

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