Autumn Books

Nature 461, 1214-1216 (29 October 2009) | doi:10.1038/4611214a; Published online 28 October 2009

Living by the calendar

Serge Daan1

BOOK REVIEWEDThe Seasons of Life: The Biological Rhythms that Living Things Need to Thrive and Survive

by Russell Foster and & Leon Kreitzman

Profile Books/Yale University Press: 2009. 320 pp. £20, $28

Living by the calendar

ILLUSTRATION BY JONATHAN BURTON.

Much of biology is governed by the seasons. Reindeer seasonally adjust the colour of their eyes for better vision; newborn warblers are programmed to fly from Europe to an unknown destiny in Africa; hibernators turn down their internal thermostat for six months of the year. Most biologists would jump to unravel such seasonal feats if the time constraints were not so forbidding. Russell Foster and Leon Kreitzman lament in their latest book the slow pace of research on annual rhythms in biology. Yet their fascinating story impresses with its wealth of facts and splendid overview.

The Seasons of Life follows on from the authors' previous collaboration, The Rhythms of Life (Profile Books, 2004). Russell Foster, a professor in circadian neuroscience at the University of Oxford, UK, is an eminent scientist in the field of chronobiology, and a passionate one. He helped to discover specific ganglion cells in the mammalian retina that perceive light intensity and are instrumental in synchronizing biological clocks. Kreitzman is a science journalist with a lucid pen. Together, they paint a broad perspective on the functions and mechanisms of biological calendars.

The authors dedicate five chapters to the adaptation of animals and plants to the seasons, and six to human seasonality. This preference for humans is unexpected, but appropriate and stimulating. Research interest in human seasonality has been considerable but necessarily of a descriptive nature. The annual rhythm of human reproduction, for example, is well known and has been recorded extensively in birth records. Evolutionary zoologists can only dream of having similar vast data sets.

Until recently, the consequences of birth date for human characteristics was a theme for astrologers rather than scientists. Database analyses now show that the incidence of a host of diseases later in life, such as schizophrenia, multiple sclerosis and suicidal behaviour, varies with the season of birth. This seasonal variation, the authors argue, holds the key to understanding the impact of environmental effects during gestation and early postnatal life on adult health and lifespan.

Living by the calendar

ILLUSTRATION BY JONATHAN BURTON.

Foster and Kreitzman mix suggestive new facts with recently recovered old references: for instance, the Babylonian king Hammurabi recommended using sunlight in the treatment of illnesses 6,000 years ago, pre-empting recent reports of the alleviation by light of depressive symptoms in seasonal affective disorder. The authors lead the reader into the literature on the systematic seasonal variations in suicide, on general mortality and on violence.

Seasonal phenomena in plants and animals are more readily approached by experimentation than are those in humans. The book tells the story of the discovery of photoperiodism — the study of the physiological changes in reaction to the length of daylight — first by Wightman Garner and Henry Allard in plants in 1920, and then by William Rowan in songbirds in 1925.

The authors also detail the finding of innate circannual clocks: endogenous seasonal rhythms that persist even in constant temperature and day length with a usual cycle length of around 300 days rather than 365 days. Circannual clocks were first found in hibernating ground squirrels by Eric Pengelley in 1966, and in seasonally migrating songbirds in 1967 by Ebo Gwinner, the influential ornithologist to whom the book is dedicated. In the 40 years since then, significant progress has been made by only a few labs. The physiology of the circannual pacemaker in the Soay sheep, for example, is becoming better understood through studies by Gerald Lincoln and David Hazlerigg at the Centre for Reproductive Biology in Edinburgh, UK.

Foster and Kreitzman have produced a tantalizing account of the facts behind seasonality. Its occasional nickname, 'nature's contraceptive', reflects the key function of seasonal organization: thousands of species across the globe, including those in the tropics, use seasonality to turn off reproduction at times of year when low food supply is expected and individual fitness is better served by waiting for the next season. The Seasons of Life is a joy to read, and a compelling text on the importance of seasonality in the evolution of life on Earth.

  1. Serge Daan holds the honorary Niko Tinbergen chair in behavioural biology at the University of Groningen, PO Box 72, 9700 AB Groningen, the Netherlands.
    Email: s.daan@rug.nl

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