Matt Ridley
Fourth Estate
320 pp

P D Smith
176 pp

On the crest of the wave of hoop-la attending the 50th anniversary of the discovery of the structure of DNA by Watson and Crick, the appearance of Matt Ridley's Nature via Nurture will be an invaluable corrective to the pernicious belief that we are the products of our genes. Indeed, Ridley's declared purpose is to demonstrate that the old argument of nature versus nurture is futile and meaningless.

This he does effectively by citing a wealth of examples from the current literature of animal (including human) behaviour, molecular biology, neuroscience and so on that demonstrate the interdependence of genotype (genetic structure) and phenotype (external appearance and behaviour) that give the lie to the all-too-common belief in genetic determinism.

It would be strange if it were otherwise. All organisms now alive have evolved by Darwinian processes, or by the effects of natural selection on the inheritable variations that Darwin first postulated in 1858. The chief contribution of modern genetics is to have identified the cause of these variations as genetic mutations (specifically, alterations of the chemical structure of inherited DNA), but sometimes including wholesale rearrangements of the genes.

The effect of natural selection on an evolving lineage is therefore to make its genetic constitution match the environment in which it finds itself. In other words, our genes and their arrangement are products of our environment. So there is a sense in which genetic determinism (We are the products of our genes) amounts to saying that we are the products of our environment or, otherwise, of nurture.

That argument (which Ridley does not use) is unfortunately over-simple. Our genes are not the product of our present environment alone, but also of all the environments our genetic ancestors experienced. There is ample room in that statement for historical accident. Why, for example, do people usually have five toes on each foot and five fingers on each hand?

There is nothing to suggest that these numbers have been fixed in people by natural selection. Rather, Ridley says, they are a manifestation of evolutionary inertia: for some ancestral amphibian, perhaps a frog of some kind, five digits may have been advantageous in the Darwinian sense.

Ridley's treatment of the role of inheritance in the determination of intelligence and, more generally, of personality, will be for many readers the touchstone by which his book is judged. The title of the relevant chapter, 'A convenient jingle', is taken from Francis Galton's description of nature and nurture as such, but well-read Ridley quotes Prospero in The Tempest as saying "A devil, a born devil, on whose nature nurture can never stick". Galton was also the first to use the study of twins (reared separately or otherwise) to sustain his belief that genius is inherited.

More recent twin studies, particularly by one Thomas Bouchard, have shown that the elements of the standard psychologists' classification of personality are closely correlated in identical twins reared separately. (In one study using questionnaires, the correlation of an index of religious fundamentalist beliefs worked out at 62 per cent for identical twins reared separately, compared with only 2 per cent for non-identical twins reared separately.)

Interestingly, there is some evidence that a particular mutation of a human gene (responsible for a protein called brain-derived neurotrophic factor) appears to be linked with what the psychologists call neuroticism, and especially with depression. Ridley emphasises that this is not the gene for depression, but that when it has been found how and where (in the brain) the protein functions, it may be a valuable clue in the search for more effective anti-depressant drugs.

The validity of twin studies, and of Bouchard's in particular, is still controversial. There are genuine uncertainties about the means by which pairs of twins are selected for study, for example. But equally, they cannot be ignored. And what they suggest for IQ is that there is a substantial genetic component, perhaps a half, but that environment is responsible for the other half. But Ridley emphasises another trend shown by the data: in an environment of poverty, environment may be the principal determinant of IQ, but riches bring out the influence of the genes.

The social implications of that state of affairs are paradoxical. First, that the safety nets that guard against poverty should be strengthened. Second, that in prosperous societies, the influence of genetics will be enhanced - the meritocracy may be a reality.

By itself, Ridley's book will not bury forever the argument about the influences of nature and nurture. There are entrenched positions on each side. But the scope of the book, which covers the whole of human behaviour and which includes an argument in favour of the reality of free will (nature and nurture notwithstanding), and the manifest care with which it has been researched, should powerfully stimulate a re-examination of these important questions.

Ridley also has an eminently sane attitude to the ferocity of past arguments about the relative influences of nature and nurture. Why, he asks, cannot the protagonists accept that their opponents' arguments, even if not entirely watertight, may nevertheless be partly correct? But the IQ wars will not be finally ended until laboratory geneticists have learned more of how genes on the one hand and the external environment on the other determine what happens in the parts of the brain that constitute mind. That task will still be incomplete by the end of this century.

Luckily for biologists (and especially for human psychologists), it is now proper to think of giving human psychology a basis in human physiology. When genetics has gone beyond the listing of all the human genes to discovering what functions they have in the development and life of people, psychology will be rescued from the doldrums into which it has fallen in recent years. The ebullience of the genetic enterprise is plain to all.

By comparison, the physical sciences appear to be going through an arid patch, with university departments unable to recruit as many students as they seek, with newspapers apparently jaded with a surfeit of spectacular photographs recovered from the Hubble Space Telescope and with a dearth of new gadgets to match the computers on our desks. But a new biography of Einstein (Einstein, by P.D. Smith) is a reminder that there is excitement waiting in the wings.

This is a pocket-sized volume running to 130 pages and probably no more than 40,000 words of text. Its novelty is that the author has read through the eight volumes of Einstein's correspondence so far published (out of an estimated total of twenty-five) and gleaned new information about Einstein's marriage (to a fellow student at Zurich), his divorce and re-marriage and his subsequent affairs. But the tale is in no way salacious, while the essence of Einstein's many achievements is faithfully if sparsely recounted.

Saving space has been such a central goal that the book lacks a preface, for which reason it is not possible to be certain what the author aims at. Even so, the innocent reader will often be bemused. For example, the distinction between Einstein's two relativity theories, of 1905 and 1915, is not as crystal clear as it should be: the first corrected Newton's laws of motion, the second was a viable alternative to Newton's theory of gravitation. And the significance of Maxwell's equations, frequently referred to, is not described so far as I could tell.

With all that said, the book will be for many readers a convenient introduction to a fascinating subject. Full length biographies of Einstein appear regularly, and get longer as the years pass. This book should be an excellent means of deciding whether to tackle such a work.

Meanwhile, what is there about relativity that promises to enliven the physical sciences? Einstein's second theory - his versions of Newton's gravitation - is the key.

Largely on the basis of the properties of the sub-atomic particles of matter discovered at the large particle-accelerating machines, it has been concluded that material particles interact by means of four different types of forces, of which gravity is ordinarily the weakest. Moreover, there has been cultivated an ambition to represent all these forces as different aspects of a single interaction. Unification is the slogan.

The sad truth is that the ambition has so far been frustrated by the difficulty of incorporating gravitation into the unified force. Another way of putting the problem is to say that gravitation and quantum mechanics (to which Einstein himself made crucial contributions before he became disillusioned with it) appear to be incompatible. So there is a search under way for a theory called quantum gravity.

When and if that is found, we shall have a different view of what the world is like. Even the Big Bang theory of the Universe may bite the dust. And Einstein's perceptiveness will yet again be confirmed.

Nature via Nurture and Einstein are available from Amazon (UK).