The Descent of the Child: Human Evolution from a New Perspective, By Elaine Morgan Souvenier Press #163;14.99 0 285 63212 4

The past decade or so has witnessed a dramatic growth in understanding of human evolution. In part, this has reflected the number of fossil specimens that has been unearthed in recent years, but in part it also reflects the impact of wonders of modern science such as molecular genetics that have revolutionised the kinds of information available to us.

In addition, advances in evolutionary theory have allowed us to glimpse beneath the surface of human ancestry to see how and why we have come to be as we are. Both these books capitalise on these new findings, though the approach and style each adopts is very different.

Caird’s Ape Man is in the more traditional style of books on fossil humans. The book, lavishly illustrated with both photographs and specially commissioned full-page paintings and drawings, was designed to accompany a television series (yet to be shown in Britain). It is simply written, opts for a coffee-table format and contains just six chapters, which deal with different aspects of what has made us who we are (our fossil history, bipedal locomotion, our giant brains, language, large-scale migrations and art); a seventh chapter looks with a less convincing hand at our evolutionary future.

The book, alternating between story-teller text and interview quotes, tries to let science tell its own story. Here is the new genetic evidence suggesting that humans and chimpanzees share a common ancestor that lived a mere five to seven million years ago; close on its heels comes the evidence that all living humans are descended from an ancestor that lived a mere 150,000 years ago.

We come face-to-face with Lucy, the four-foot-high fossil drowned in what might have been a flash flood in a Ethiopian watercourse 3.3 million years ago. We meet the Nariokotome Boy who, aged just 11 when he died on the shore of Kenya’s Lake Turkana 1.75 million years ago, was already five foot three inches tall. By applying techniques rather similar to tree-ring dating to teeth, it has been possible to establish that his true age at death was 11 years, rather than the 15 years suggested by his physical size: he and his kind grew faster than is the case with modern humans but slower than is typical of living apes.

In contrast to this feast for the eye, Elaine Morgan’s The Descent of the Child is a feast for the mind. It eschews the hard evidence of human evolution in favour of the insights that Darwinian evolutionary theory has given us into our behaviour and its origins. Morgan, a writer with impeccable credentials and a wonderfully intimate style, has attracted a significant following for her more serious books in the decades since she published The Descent of Woman.

The Descent of the Child takes the unusual angle of an evolutionary perspective to follow through the human life story from conception to parenthood. Where Caird’s Ape Man answers questions of how and when the story of human evolution unfolded, this books asks and answers questions as to why we are the way we are.

On the way, it presents an extraordinary lucid account of current evolutionary thinking on questions like why we have two sexes (still widely regarded as the greatest mystery in biology), parent-offspring conflict and parental investment decisions. She tackles with tactful firmness some of the areas such as infanticide that many outside evolutionary biology find profoundly disturbing.

We have always assumed that the business of reproduction is a matter both of joy for the parents and of co-operation between parent and offspring, but studies of animal behaviour and the mathematics of evolutionary processes have shown that real life is not so cosy: parent(s) and offspring are locked into a conflict of partially overlapping interests that begins as early as the moment of conception. It finds expression in the way the foetus chemically blocks the mother’s immune system so as to prevent its own abortion, as well as the way its suckling prevents the mother’s return to menstrual cycling (so staving off the risk of competition from a new sibling for the mother’s limited energy resources).

On the other hand, the arrival of a new infant is not always a matter of joy for its parent(s). Among the historical Eskimo, an extra mouth to feed could place the rest of the family’s survival in jeopardy. In such cases, infanticide, whether by deliberate exposure or by benign neglect, was a common solution to a difficult decision in which short-term joys must be balanced against long-term costs.

Biology makes no apologies for its sometimes shocking findings. Evolution provides no guarantees that all is for the best in the best of all possible worlds (to quote Voltaire’s buffoonish Dr Pangloss). We need to learn to view ourselves dispassionately rather than, as we so often do, the way we would prefer ourselves to be.

Nonetheless, the story that Elaine Morgan tells is both hopeful and redolent with the wonder of the greatest of all miracles, the generation of new life and its gradual development into an adult human.

This is a wonderful little book. Give one to every school-leaver.

Robin Dunbar is professor of psychology at the University of Liverpool.