Product of one imagination

Some emerging disciplines attempt to unify disparate approaches, in the expectation that the whole will be greater than the sum of its parts. Evolutionary psychology is one such discipline and, in recent decades, much has been achieved in it despite critical carpings from many sociologists, psychologists and biologists.

Two books stand out in my mind as useful for undergraduates taking courses in evolutionary psychology. The first is by Christopher Badcock, a sociologist, who provides an accurate, readable introductory text ( Evolutionary Psychology , 2002). The second, by Kevin Laland and Gillian Brown, is a more historical account that analyses different ways of tackling the subject and thereby identifies the different schools of thought that are being unified ( Sense and Nonsense: Evolutionary Perspectives on Human Behaviour , 2002).

This new book by Louise Barrett, Robin Dunbar and John Lycett aims to be more comprehensive than these two. But although it is a product of considerable industry, I cannot recommend it to an undergraduate or a teacher.

The main reason lies in its lack of rigour. From the beginning, evolutionary psychology has run the risk of being a particularly soft science. Early problems were, as the authors recognise, "adaptive storytelling" (make an observation and then provide a Darwinian explanation for it) and "progressive ad hoc optimisation" (add new parameters until an observation fits a Darwinian explanation).

Their text argues for pluralism in order to include non-adaptationist explanations, but all too frequently it does not practise what it preaches. Similarly, there is a plea for mathematical formalism to underpin scientific explanations, but I could find only one very minor model developed in the whole book.

Instead, apparent patterns in weak data sets are described, usually without sample sizes, and the results provided with verbal explanations that may or may not be correct. It may be fun to analyse lonely-hearts advertisements to reveal patterns of published expectation for people of different claimed sexes and ages, but to seek to draw evolutionary conclusions is all but useless because the lack of scientific controls beggars belief.

It is probably even less useful to analyse Norse sagas as providing scientific evidence for kin selection. The book acknowledges that "the events and motives (the sagas) describe may be completely fictitious" but then claims that the author(s) must have inhabited a world where kin selection seemed appropriate.

If analysis of Agatha Christie's novels went against the expectations of kin selection, presumably it would be ignored or she would be described as abnormal. I am sure this textbook would not conclude that she inhabited a world bereft of kin selection. The problem is compounded throughout the book by scores of figures that lack error bars (and usually any statistical analysis), so the student cannot know what to believe.

Finally, at first sight the book appears reasonably comprehensive in its treatment of a considerable literature, except that "Dunbar" appears rather frequently. In fact, papers by this particular co-author of the book are cited (according to the author index) on about 100 pages of a 383-page book, which is more than four times the citation rate of any other author.

This book presents the world according to Robin Dunbar, ignoring intellectual giants who have established and developed the scientifically respectable foundations of evolutionary psychology. Their contributions merit the balanced and proper treatments that the books by Badcock, and Laland and Brown provide.

The more comprehensive text remains to be written.

Paul Harvey is head of zoology, University of Oxford.