NATURE|Vol 445|8 February 2007 BOOKS & ARTS

A big bite of the past By standing up for themselves between 3 million

and 4 million years ago, and her fellow READER/SPL J. afarensis caused quite a stir. But is just one factor in the rich mix of evolution, as amply shown in the revised, updated and expanded From Lucy to Language (Simon & Schuster, $65). Donald Johanson, who discovered Lucy, and his co-writer Blake Edgar have added the big finds since 1996 to their brilliant overview, including the Indonesian ‘hobbit’ Homo floresiensis. And as this snap of A. afarensis teeth from reveals, the expanded range of photos — many at actual size — remain jaw-droppingly spectacular. B.K.

in biology makes sense except in the light of Back to basics evolution. The various molecules in cells and the gene sequences of the macromolecules are adapted function. This, Mayr argued, resulted products of previous selection by which their Darwinian Reductionism: Or, How to Stop in the autonomy of biology with respect to proximately causal (structural and functional) Worrying and Love Molecular Biology by Alex Rosenberg the physical sciences. Alex Rosenberg’s book properties were screened. In bringing causal- Press: 2006. 272 pp. Darwinian Reductionism is a response to the ity to bear on explanation, he makes use of the $40, £25.50 anti-reductionist position in contemporary distinction between ‘how possible’ and ‘why philosophy of biology and to the autonomist necessary’ explanations. Ultimate historical Bruce H. Weber stance of some biologists. explanations of current biological structures The understanding we have gained about the Rosenberg’s thesis is that biological phenom- and functions are ‘how possible’ in type. But molecular basis of living systems and their ena, including their functional aspects, are best why particular molecular arrangements were processes was a triumph of twentieth-century understood at the level of their macromolecu- selected in the past has the force of ‘why nec- science. Since the structure of DNA was eluci- lar constituents and their interactions in cel- essary’ explanation. This removes the burden dated in 1953, molecular biologists have been lular environments that are themselves made from selectional dynamics of having to be pre- deepening our insights into a wide range of bio- up of other molecules. This has been, and con- dictive in order to be reductionist. logical phenomena. It has been a heady time: tinues to be, he argues, a successful, progressive Rosenberg realizes that theory reductionism it seemed that mendelian genetics would be research programme. He focuses in particular requires the theory of darwinian natural selec- reduced to the macromolecular chemistry of on the great advances in our understanding tion to be grounded in, or reduced to, a princi- nucleic acids, with biology set to become a of developmental molecular biology, which ple of natural selection at the level of chemical mature science in the same way as physics and teaches us how the genes that are involved in systems in which both stability and replica- chemistry. The emerging field of the philoso- development function, interact and work with bility are selected for. In effect, he produces a phy of biology inherited the reductionist chemical gradients, for example, to produce scenario in which biological selection can be framework of logical empiricism. But as our morphology. Rosenberg provides an accessible reduced to chemical selection during the origin knowledge of molecular biology deepened, review of current ideas on the ‘wiring’ of such of life. This crucial move needs more careful many philosophers of biology, including David gene complexes and the way they help account analysis than Rosenberg provides. He gives, Hull, Philip Kitcher, Eliot Sober, Evelyn Fox- for morphological evolution. He is one of the in effect, a ‘how possible’ explanation for the Keller and Paul Griffiths, saw that the reduc- first philosophers to consider the implications emergence of life and biological selection, but tionist approach faced serious problems. of ‘evo-devo’ (evolutionary developmental not a ‘why necessary’ one. For that he would There is no simple correlation between the biology), and seizes the opportunity to promote need to deal with the literature of the origin of mendelian gene and the increasingly complex a reductionist interpretation that was simply life and the more general recent work on com- picture provided by molecular genetics. To not possible with population genetics. plexity. Such an investigation would show that make matters worse, the theory to be reduced He shows a good grasp of the scientific phenomena in these areas are more emergent was presumably the population-genetic version details of developmental molecular biology, than Rosenberg believes, and that there is a of darwinian natural selection, which had from but it is unfortunate that in the introduction need to develop a theory of organization and the start excluded phenomena about develop- he gets the molecular details of sickle-cell emergence. Research on emergent complexity ment and their possible link to evolutionary anaemia wrong and then describes a result- is still a work in progress, but it may undercut dynamics. Given this absence, Ernst Mayr, a ing arterial blockage, rather than the lysis of Rosenberg’s thesis by providing a fully natural- founder of the modern evolutionary synthesis, red blood cells. This should not have survived istic, non-reductionist account of emergence. argued that, although biological systems did the reviewing and editing process, but it is the Such a non-reductionist account would not be not violate the laws of chemistry and physics, only serious lapse. When he returns to the issue anti-reductionist in the sense Rosenberg uses evolving biological systems have properties of mutant haemoglobins later in the book, the term, but would offer a ‘why necessary’ that cannot be reduced to such laws. The crux he gets the molecular details for sickle-cell explanation of the emergent phenomena. ■ of the issue as Mayr saw it was that, whereas the haemoglobin correct. Bruce H. Weber is emeritus professor in the physical sciences deal only in proximate expla- To bridge Mayr’s gap between ultimate (nat- Department of Chemistry and Biochemistry, nations, the biological sciences also deal with ural selection) causes and proximate (struc- California State University, Fullerton, and in ultimate explanations relating to evolutionary tural and functional) causes, Rosenberg cites the Division of Science and Natural Philosophy, descent and the action of selection to produce Theodosius Dobzhansky’s dictum that nothing Bennington College, Bennington, Vermont, USA.

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