Did the chicks fly the nest or were they pushed?

The generation of evolutionists after Charles Darwin had little trouble identifying conflict in the biological world. Despite the occasional rhetorical flourishes in On the Origin of Species , and Darwin's care in making his prize concept of natural selection an agent of ultimate good, his vision was one of sharp Malthusian competition and, therefore, struggle. Conflict can occur between different species of organisms as members compete for space, food and other necessities; and between individuals of the same species as they jostle for these same things, as well as for mates. Darwin's theory of sexual selection supplemented that of the more fundamental one of natural selection.

His evolutionary work did not rely on any particular mechanism of heredity; it required only that some variations were inherited. With the rise of genetics in the 20th century, his theories were refined, and the precise nature of kinship between members of the same species became better understood. Altruism, rather than conflict, became a central biological puzzle, albeit one that Darwin had recognised in the social insects such as ants, bees and wasps, where hundreds of asexual workers devote themselves to the greater good of the colony (and, ultimately, the reproductive queen).

The issue of biological altruism was elucidated in the 1960s by William Hamilton, who analysed the genetic relationships between individuals within social insect communities. The discovery that altruism might make genetic sense to drones destined never to reproduce fuelled the then-nascent discipline of sociobiology, much more contentious a generation ago than it is now. Game theory and sophisticated mathematical modelling are now employed to provide theoretical frameworks for understanding the behaviour of organisms, plant as well as animal. Biological notions of altruism are based on a premise that Darwin would have recognised had he the advantage of modern genetic knowledge: it makes evolutionary sense for an organism to ensure that its genes are passed to the next generation, by whatever strategy is appropriate to the peculiar circumstances of the species in question. This does not always involve every individual reproducing.

Douglas Mock's engaging volume assimilates the vast literature on altruism but concentrates on the more traditional analysis of conflict. He thus returns to the old question that Malthus posed and Darwin answered: why does reproductive capacity outstrip the reality of survival? Darwin offered the general answer of natural selection. Armed with modern genetics, theoretical biology and field observations, Mock refines the question, and focuses on families. When birds lay three or four eggs, and only a couple of fledglings survive each season, what are the family dynamics involved? Why do parent birds often watch, and sometimes even participate in, the passive or active murder of one or more of their offspring? Does birth order matter?

As befits a modern evolutionary biologist, Mock offers no ultimate answers: nature is as it is because it is conditioned by what the ancient Greek philosopher Heraclitus long ago called chance and necessity. Mock concentrates on his own speciality, birds, and describes a number of scenarios of how different species of birds regulate their numbers, in direct or indirect response to environmental conditions. Egrets, penguins, gulls, eagles and blackbirds feature prominently, and cuckoos make their appearance. Unsurprisingly, perhaps, birds adopt a number of strategies to ensure that their genes are perpetuated. Most of the examples Mock discusses involve what can anthropomorphically be called cruelty.

Mock's monograph demonstrates triumphantly that field studies are still a vibrant part of evolutionary biology. He is equally entertaining about his own field studies and those of others engaged in testing in the field the models of theoretical evolutionary biology. Sometimes he and his colleagues resort to experiments, such as placing additional eggs or young birds in nests; more often, they simply patiently watch feeding practices and aggression within the nest and interpret what they see in the light of other observations or theoretical predictions. As in all areas of good science, observations modify theories and theories direct observation.

Mock's is one of those sought-after books in science, a work of popularisation and a thoughtful synthesis of an important discipline. It lacks only an analysis of the language that Mock uses to describe his birds. He sticks to his early promise to avoid jargon, but he never tells us whether words and phrases such as "insurance policy", "upgrading the kids" and the like are to be taken as having human significance. He dedicates his book to his three elder brothers (he was the "D chick"), but he never reflects on whether this book is an essay in sociobiology or a monograph about evolutionary ornithology. If the two are the same, he ought to come clean.

W. F. Bynum is emeritus professor of the history of medicine, University College London.