Survival of the myopic

Imagine humans with eyes in the back of their heads to give rear vision or an extra ear on the top of their head to enable better vertical sound discrimination. This book, with a refreshingly new approach among popular books about evolution dwells on the imperfections of the evolutionary process. Once evolution is committed to a certain development pathway it is not always possible to reverse it as further adaptation occurs. In the early development of land-dwelling vertebrates a pelvic ring of bone evolved through which the digestive, reproductive and excretory systems all pass. As a result human babies have to squeeze through an extremely narrow space that makes human birth more difficult than that of most other mammals. Why have we not evolved an opening between the pelvis and the ribs, the area that is used by surgeons for caesarean deliveries? The author also refers to the "nonsensical association" between systems for reproduction and excretion in humans and apes so that in the case of males, sperm and urine are evacuated through the same tube. The unnecessarily long tube to convey semen from the testis to the penis, wrapped over the ureter instead of following a shorter and more direct route, is termed a "functional absurdity" by George C. Williams. Mammals are designed with the possibility of choking because the air passage and the digestive systems have to cross over each other. These and other design flaws in the human body are used to demonstrate that natural selection, concerned only with what is slightly more adaptive here and now, does not necessarily produce the best design for the future.

It is good to read about evolution as interpreted by someone other than Richard Dawkins (who has done so much to explain the evolutionary process and whose book River out of Eden appears in the same Science Masters series as the current volume). The watchmaker of William Paley and the wonders of the human eye appear here too, but in addition to explaining the eye through the process of evolution, Williams points out the defects in the design that led to such problems as detached retinas. Not all the features of the human eye make functional sense. The eye has a blind spot where the optic nerve exits through a hole in the retina but it would not if the nerve fibres passed through the sclera and formed the optic nerve from behind the eye as happens in the eye of a squid. However, because of the gradual process of natural selection our eyes, and those of all other vertebrates, have the "functionally stupid" upside-down orientation of the retina. The process of evolution has produced many functionally elegant features but also has a historic burden of various dysfunctional or far-from-optimal features. Evolution has a controlling mechanism that favours the elimination of disadvantageous characters often giving long-term stability rather than continual change. As an example, take the 1899 observations of Herman Bumpus who measured the wings of a large number of sparrows that had been killed by a fierce storm. He found that those with wings markedly longer or shorter than the average were more abundant among those killed than in the population at large. Much of the selection that takes place in nature is of this normalising type that produces stability rather than that which causes a shift in average values from one generation to the next. By showing both the favourable and the less favourable aspects of evolution through natural selection we have here a book that presents a balanced and easy-to-understand explanation of the processes involved.

One of the applications of this approach to evolution is what the author has termed "Darwinian medicine". The understanding and the explanation of many of our medical problems is through the understanding of how our systems have evolved and of the consequent design flaws that are built into our bodies. One of the wonders of evolution is the defenses which our bodies have against disease. When a human suffers a Streptococcus infection the result may be headache, sore throat, fever and anaemia. These are not simply the result of the bacteria but more the result of our defence against it: the headache makes you want to relax and avoid stress, thus hastening recovery, the sore throat means you want to be careful about what you swallow, the fever facilitates immunological response and anaemia deprives the bacteria of a nutrient. Often the treatments we use combat our natural defences against an infection. Through an understanding of why we have a fever or anaemia more appropriate medical treatment can be given. The author argues that the medical profession gives little thought to what is adaptive and maladaptive for the patient or the pathogen. The iron prescribed to treat the anaemia may be just what the bacteria need to thrive.

The human species is one that is really adapted to stone age conditions rather than our modern environment. In the stone age it was advantageous to seek foods that were sweet and rich and maximise the intake of sugar and fat led to health and vigour. This craving for sweet and fatty substances, which was an adaptive advantage in the stone age, has led many contemporary humans to ill health through obesity, diabetes and heart problems. With our sedentary life and excessive calorie intake our stone age desire for these foods is detrimental to our health.

This book presents a strong call for the use of Darwinian insights to treat mental disorders, allergy, cancer, sexual and reproductive dysfunction and many other disorders and the author believes that the study of evolution will soon be recognised as an indispensable foundation for medical science. On one aspect I question his argument. He thinks that the myopia and dental problems which are so rife today have arisen from our abnormal usage of our eyes and our teeth during childhood and adolescence. I think it is more likely that we have side-stepped the process of natural selection. The stone age hunter who could not see the game was clearly at a disadvantage and was less likely to survive. Today our scientific skills can restore reasonable vision to even the most strongly short-sighted individual. As a result this trait is passed from one generation to the next rather than being weeded out by natural selection.

The final chapter on the philosophical implications of the author's approach to evolution makes good reading. Unlike Dawkins he is not promoting atheism, but on the other hand he is not in agreement with the claims of Paley that God is a master engineer. The author's deep understanding of nature has shown him the cruel side, and the constant battle of predator versus prey. His God is not all good. This book demonstrates that an understanding of evolution is vital for a true understanding of human life and for the solving of both medical and environmental problems.

Sir Ghillean Prance is director, Royal Botanic Gardens, Kew.