Sean B. Carroll
(Princeton University Press, 2016); hbk, £16.95
The Serengeti Rules is a an excellent book on ecology written by a molecular biologist, S B Carroll, in which he links mechanisms of control found at the molecular level with the factors determining the relative numbers of plants and animals living together in ecosystems. The decisions of policy makers and funders over thirty years have unbalanced the discipline of biology in our universities, making it almost entirely molecular genetics, and leading to the neglect of macrobiological studies. More importantly though, Carroll tells us that we now possess the basic scientific knowledge – he calls them the “Serengeti Rules” – to assist the recovery and restoration of damaged ecosystems.
The book starts with Walter Cannon, an American physiologist who saw that animals have an astonishing ability to maintain critical functions within narrow survival ranges; depart from these and serious disease follows. For instance, insulin allows us to keep blood sugar levels within safe bounds; failure of this control system results in diabetes. Cannon came to see that regulation might be the “central matter of physiology”, “that abnormal regulation is the central issue in medicine”. The work of Jacques Monod introduces molecular biology. Monod and Francois Jacob won the 1965 Nobel Prize for their work on the regulation of enzyme synthesis in bacteria. They discovered that there are two kinds of proteins in cells: structural proteins which carry out chemical reactions or build up cell structure and regulatory proteins which control the production of structural proteins. Monod also demonstrated what Carroll calls “double-negative logic”, where lactose induces the production of an enzyme (beta-galactosidase) which allows the bacterium to use it as a food source, not by stimulating its production directly, but by inhibiting the production of another enzyme that represses the production of beta-galactosidase. The “double-negative logic”process can also be seen in ecosystems. In Alaskan marine communities, the presence or absence of sea otters determines the amount of seaweeds in the area; otters prey on sea urchins which eat the seaweeds, thus effectively also controlling the proliferation of seaweeds.
The ecological story is thus interwoven with the molecular story. This intertwining begins with the work of Charles Elton, who was the first to draw a “food web” which shows who eats whom in an ecosystem. Elton derived some of the basic principles of ecology from this concept of food webs and chains. For instance there is the “pyramid of numbers”: abundant plants at the bottom, large numbers of herbivorous insects, large but smaller numbers of carnivorous insects and so on, ending with very small numbers of large predatory animals at the top of a a food chain; .
This relatively short book contains many more explanations of molecular and ecological science. Carroll also provides fascinating background on the scientists who did the work, many of whom should be better known. Jacques Monod carrying on research in wartime Paris while actively working in the French Resistance, and Janet Davidson’s struggles to carry out and publish pioneering research on the genetics of leukaemia while simultaneously bringing up a family of four, are particularly memorable stories.
Carroll’s analogies between control at the two opposite ends of life – the ecological and the molecular – are convincing, given that the regulatory mechanisms do indeed appear to be the same. To finish, Carroll brings together case studies of successful interventions in damaged ecosystems in the US and Africa, closing finally with a call to action, inspired by the successful eradication of smallpox throughout the world by 1980.
The Serengeti Rules should be widely read. The only drawback of the book is that it tells us that our own human numbers (7 billion and rising) have already exceeded the regenerative capacity of the earth. This fundamental problem is not addressed in his closing “Rules to Live By” section, nor is the related issue of global warming addressed