Like books along a bookshelf
- The Wisdom of the Genes by Christopher Wills
Oxford, 351 pp, £6.99, January 1991, ISBN 0 19 286113 1
The inherited instructions by which a body is built are carried from parent to offspring in molecular form, in the DNA. The instructions come in units, called genes, and for most purposes the DNA can he imagined as a long row of genes, arranged like books along a bookshelf. It is not known exactly how many genes are used to build a human body, but the number is between 100,000 and a million, and is probably nearer the former. Evolution (on this simple conception of the DNA) happens when the environment changes and one form of a gene rather than another builds a better body in the new conditions, or when a gene mutates to an improved form. Either way, natural selection favours the superior form of the gene, which becomes more numerous. Evolution in this sense means a change in gene frequency. It is a powerful way of thinking about evolution, and evolutionary biologists use it all the time. Taking one gene at a time, they study (or, at a more rarefied theoretical level, imagine) different forms of the gene, and see how natural selection works on them.
Like all good things, however, it has its critics, Ernst Mayr, for instance, strongly objects to it. He says it makes evolution seem like changing the bean composition in a beanbag, and refers to it derisively as ‘beanbag genetics’. One of Mayr’s ‘beanbag’ geneticists was J.B.S. Haldane – and one year before his death Haldane still knew how to conduct a controversy. He ironically adopted Mayr’s term, and showed how the beanbag model had led to almost all our understanding of evolution. Thirty years later, much the same still applies. Mayr’s mistake was to confuse a cartoon with a portrait. Scientists make simplifying assumptions on purpose, in order to identify the essence of a problem and eliminate the unnecessary detail; their models do not attempt to describe nature accurately, in all its complexity. When they learn how to handle sonic previously ignored feature of nature, it can be built into a model soon enough. Meanwhile, not much is to be gained by talk, particularly if it is stuffed with slogans about reductionism and holism.
Christopher Wills is completely secure with genetic theory, and makes no attempt to belittle the beanbag model. The Wisdom of the Genes, a generally admirable book, suggests how modern genetics is leading evolutionary biologists away from the beanbag model, to think instead about how genes are organised in our DNA. Evolution has not scattered the genes in any old order, but like a wise librarian has ordered the genes in subtle schemes which enable them to operate more efficiently. Genes (unlike the contents of books) evolve through time, and Wills suggests that some genes are arranged in such a way that they can change to form new types of body more rapidly. Such is the ‘wisdom of the genes’. Wills, by the way, can be rather erratic on history: in the case of beanbag genetics, he credits the term to Haldane and ignores the ironic borrowing from Mayr. Wills thus effectively distances himself from the earlier critics of beanbag genetics – and that is undoubtedly the best relationship to have with them.