Genes and Memes
John Maynard Smith
- BuyThe Extended Phenotype by Richard Dawkins
Freeman, 307 pp, £9.95, December 1981, ISBN 0 7167 1358 6
The Extended Phenotype is a sequel to The Selfish Gene. Although Dawkins has aimed his second book primarily at professional biologists, he writes so clearly that it could be understood by anyone prepared to make a serious effort. The Selfish Gene was unusual in that, although written as a popular account, it made an original contribution to biology. Further, the contribution itself was of an unusual kind. Unlike David Lack’s classic Life of the Robin – also an original contribution in popular form – The Selfish Gene reports no new facts. Nor does it contain any new mathematical models – indeed it contains no mathematics at all. What it does offer is a new world view.
Although the book has been widely read and enjoyed, it has also aroused strong hostility. Much of this hostility arises, I believe, from misunderstanding, or rather, from several misunderstandings. Of these, the most fundamental is a failure to understand what the book is about. It is a book about the evolutionary process – it is not about morals, or about politics, or about the human sciences. If you are not interested in how evolution came about, and cannot conceive how anyone could be seriously concerned about anything other than human affairs, then do not read it: it will only make you needlessly angry.
Assuming, however, that you are interested in evolution, a good way to understand what Dawkins is up to is to grasp the nature of the debates which were going on between evolutionary biologists during the 1960s and 1970s. These concerned two related topics, ‘group selection’ and ‘kin selection’. The ‘group selection’ debate was sparked off by Wynne-Edwards’s book, Animal Dispersion in relation to Social Behaviour. Its thesis is that animals regulate their own numbers behaviourally, rather than being passively regulated by food. Wynne-Edwards further suggested that animals have evolved special displays, usually involving social aggregations (black-cock leks, shearwater rafts, the mass aerial dances of mosquitoes), which inform them of their numbers, so that they can respond by breeding if numbers are low and by refraining if numbers are high. He noted that the entity which would benefit was the whole population, which would not outrun its food supply, and not the individual, which would leave more progeny if it continued to breed regardless of numbers. He therefore suggested that the necessary behavioural adaptations had evolved by ‘group selection’ – i.e. through the survival of some groups and the extinction of others. Most biologists have doubted whether such a process could actually be effective, and have argued that natural selection typically acts by favouring some individuals rather than others, and not some populations rather than others. However, Wynne-Edwards did raise in a particularly clear way the question of the level at which selection acts – individual, population, species or ecosystem.
At almost the same time, W.D. Hamilton raised another question about how natural selection acts. He pointed out that if a gene were to cause its possessor to sacrifice its life in order to save the lives of several relatives, there might be more copies of the gene present afterwards than if the sacrifice had not been made, because relatives might carry copies of the gene inherited from a common ancestor. The suggestion has obvious relevance for the evolution of social behaviour. To model the process quantitatively, Hamilton introduced the concept of ‘inclusive fitness’. To understand this, you must first appreciate that scientists use the word ‘fitness’, as they do ‘force’, in a technical sense only loosely related to its colloquial meaning. ‘Fitness’ is a property of a ‘genotype’ – that is, of individuals of a particular genetic constitution. Crudely, it is the expected number of offspring produced by individuals of a given genotype in a given environment. Hamilton saw that to use fitness in this sense could lead to wrong predictions about how the frequencies of genes in populations would change – i.e. about evolution. He therefore replaced this classical fitness by ‘inclusive fitness’, which includes, not only an individual’s own offspring, but any additional offspring raised by relatives with the help of that individual, appropriately scaled by the degree of relationship: for example, if I (or more precisely, people with a genotype like mine) help my sister to raise a child she would not otherwise have, that raises my inclusive fitness by one half. It has since become a rule of thumb among students of social behaviour to say that animals will behave so as to maximise their inclusive fitness.
The full text of this book review is only available to subscribers of the London Review of Books.