Consider the very essence of a man

We have here 12 essays by different hands providing different answers to the question: What it is about human beings that makes them different from even their closest cousins, the chimpanzees?

Geneticist Walter Bodmer, who more than ten years ago was greatly involved in explaining the Human Genome Project to the general public, stands somewhat apart from the other distinguished contributors. His foreword is extremely helpful to the lay reader for whom the book is intended. It would be difficult without his guidance to pick through the fascinating but tangled forest of genetic, anthropological and theological speculation that the essays contain.

For it is sometimes difficult to be sure what kind of question is being addressed. Is it a scientific question, depending for its answer on the variability of genes and neurons? Is it historical - when and in what manner did Homo sapiens become crucially different from the Neanderthals who died out? Or is it a phenomenological question, such as Sartre asked: what, here and now, is the crucial difference between being human and being any other natural or manufactured thing? This is a question familiar to philosophers. Locke, for example, answered it confidently in 1690 in his Essay Concerning Human Understanding. "Brutes," he wrote, "abstract not." And therefore they have no language, most of which consists of general terms. This is the crucial difference.

The first essay in the book, by Susan Blackmore, is as confident as Locke. "To be human," she writes, "is to imitate," and she argues that human life is culturally dependent on memes: ideas, habits or gestures that infiltrate like viruses through a population. The word was introduced into the language of sociobiology by Richard Dawkins, and he, to whom Blackmore acknowledges a debt, pressed the analogy with genes, thus putting a scientific spin on a recognisable human phenomenon - fashion, or the craze.

In contrast, Richard Wrangham places learning to cook at the centre of the evolution from ape to man. He argues that not only did cooking make food more palatable but that it also had evolutionary consequences on our guts and teeth. But as to when this discovery took place, he remains agnostic.

In between these alphabetical parameters, there are essays that suggest, in various ways, that it is man's ability to imagine things not in front of his eyes - the past, the future and life after death - that places him in a class of his own. This is what Sartre called man's emptiness; his ability to grasp what is not, as well as what is. Lewis Wolpert, on the other hand, holds that the essential difference between us and the rest is our understanding of causation, our certainty that one moving billiard ball, making contact with another, will cause that other to move (the very belief in "force efficacy and power" that David Hume argued was nothing but a bit of human imagining).

There is a feast of philosophy here. But it is easy to become bewildered by the variety of assertions. It is useful, therefore, to read Bodmer's foreword as an afterword. Although human beings, we now know, share as many as 99 per cent of protein coding genes with chimpanzees, that still leaves as many as 250 genes whose difference contribute to the vastly greater "cognitive competence" of human beings compared with other animals. There is no such thing as a "gene for" any specific characteristic. What has to be sought is the variation in those sequences of genes unique to human animals, causing the changes in the brain that resulted in increased cognitive competence. All the suggested differentiating characteristics of man, to be a religious, a cooking, a cause-conscious or an imaginative animal, can be subsumed under the heading "cognitive competence". If we could discover exactly how these gene sequences worked, perhaps, if we chose, we could one day turn chimpanzees into our brothers.