One of the charms of coming with a Darwinian eye to the study of organisms is recognizing the mixture they display of astonishing adaptive sophistication and botched improvisation. For a long time one of the most persuasive arguments for the existence of God was the so-called Argument from Design: the idea that the finely tuned structures of organisms simply could not have come into existence by chance, and must therefore be evidence for the existence of an unimaginably powerful and intelligent creator. Once Darwin's theory of evolution by natural selection had proposed a mechanism by which such structures might result from purely natural and unplanned processes, what increasingly impressed biologists was the extent to which organisms turned out - despite being miracles of coordination and functioning - to be riddled with absurdities that no self-respecting designer would have allowed as far as the drawing board. Darwinian evolution does not work by planning from scratch with some end in view. The organisms produced by natural selection are merely the ones that happen to keep reproducing in the environments where they happen to be, and selection has nothing to work on but chance variations in structures that have previously been selected, often for quite different purposes. The result is that organisms carry with them fossils of their design history - which is why there has been so much success in tracing that history.
This fact provides a rather pleasing coincidence between this book and the Darwinian organisms that are its starting point. This is not, I hasten to say, in its being unplanned or the kind of thing any self-respecting designer would disown (an analogy need not work on all fronts), but in being rather different from what it would have been if it had been planned from scratch as an argument for its main thesis. And it is worth mentioning this because, as again Darwinians know very well, what looks odd or inexplicable if you approach it with one set of presuppositions may not only make perfect sense if you start from a different point, but also reveal elements that might otherwise have been invisible.
The book is, as its title implies, a contribution to the current Darwinian debate, whose main focus is the implications of the Darwinian revolution for our understanding of what we are and where we fit into the scheme of things. Everybody knows, because it is part of the legend, that Darwin's theory came as a horrible shock to the respectable Victorians on whom it was let loose, because this radically new account of their origins was so totally at odds with their own self-image. Everybody also knows - if only because of the recurring headlines about American schools that try to banish evolution from the curriculum, or insist that it is taught as 'only a theory' along with 'creation science' - that there are places where this horror is still felt, and where the Darwinian account of human origins is as strenuously resisted as ever. But it may be less clear, because there is such confusion in the public debate, that even where evolutionary theory is not resisted in its entirety, a modified version of the same controversy still continues. Many people who are by now resigned to the idea of our biological