Review of Henry Gee, 'Deep Time: Cladistics, the Revolution in Evolution' (Fourth Estate, 2000).
This review first appeared in the Critical Cafe, 9 November 2001.
I recommend this book on two grounds. Firstly, it is an excellent account of a method that challenges many widely-held misconceptions about evolution. Secondly, though, it is a model of what a book - or method - based on critical rationalism should be.
This second point may come as a surprise to the author himself (a Senior Editor on the scientific journal Nature). I do not recall that he mentions Karl Popper (there is no entry in the index) and he certainly does not use the term 'critical rationalism'. Yet there are the signs of a CR approach throughout: the testing of hypotheses against the evidence, with falsification in mind; alternative conjectures placed against long-accepted explanations; and a strong cautionary tale of how theory can outstrip the limited data available. It would be very interesting as a historical exercise to find out whether CR did at all inspire the founders of cladistics, but it may soon be too late as some of them are already dead.
Cladistics itself is a methodology for classifying and relating both living things and fossils, based strictly on the similarities and differences between them. It makes no assumptions about the descent of one species from another: as Gee points out, geological time ('Deep Time') cannot ever allow us to answer such questions, because the fossil record is fragmentary and disconnected, depending both on the remote chance that an organism will be fossilised, and the remote chance that we shall uncover it. Even if we happen to uncover the fossil ancestor of a living organism or another fossil, there is no way we can ever recognise it as such.
What cladistics did do is falsify some of the cherished theories that were common in the study of evolution until the 1980s, maybe even now, and are still reflected in much of the popular idea of evolution today. The key misconceptions, which Gee identifies as having roots in the origins of evolutionary theory, are the idea of a static 'archetype' of a species; the idea of evolution as 'progress' or 'a great chain of being', 'culminating' in the human species; and the assumption that a characteristic of a species must have evolved 'for' the purpose for which it is used now. These have led to models of evolutionary paths that have constrained the thought of researchers, distorting the way in which they have interpreted later fossil finds.
Gee explores the application of cladistics to three major problems: the palaeontology of fishes and the ancestry of land-dwelling tetrapods (he himself worked in this field with some of the founders of cladistics as a young researcher); the relationships between birds and dinosaurs and the origin of flight; and human evolution. The results are surprising and intriguing. They are also deeply unsatisfying to anyone who thinks that science should deliver a continuous and consistent story about evolution, but that's the way it is.
If I have any reservation about the book, it is that Gee tends sometimes to be overlong and repetitive. When he does repeat himself, though, it is an important point he is trying to emphasise. Although he explains the fundamentals of a cladogram at great length, using examples like Henry and his two cats (and a pigeon), when he discusses the relationships of individual species in his arguments later in the book, he appears to leave some of the steps implied for the reader to work out. A few more cladograms here might have been helpful.
Beyond the immediate subject, this book should inspire people working in other fields. One of the things about palaeontology is the sparseness of the data: fragments of skeletons preserved and discovered by pure chance, and then over-interpreted by the theorists, huge stories hung on meagre bones. Cladistics helps to falsify and disperse this accretion of theory. In so doing, it brings out the role of contingency in the way evolution has actually occurred on this planet, as is emphasised by the chapter on birds and dinosaurs.
Other subjects also suffer this problem of sparse data with a strongly non-deterministic origin. One is economics: there is only one economy, but it is a massively multi-dimensional system. For data, economists can study only very limited sections on specific lines or surfaces within this whole model. Yet, on these tiny fragments of data hang huge sheets of theory, such as the theological disputes of the keynesians and anti-keynesians, and the rigid determinism of the marxists and neoclassical liberals. It could be a critical-rationalist aim to develop a tool that does for economics what cladistics does for palaeontology.
Copyright © 1999-2002 Richard Burnham