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and Oxford. 709 pp. f 17.95 (pbk). ISBN 0-1 9-50581 1-9 and ISBN 0-1 9-507951 -5 (pbk). Most contemporary evolutionary biologists would agree with these statements. The application of genetic principles to the study of the population processes which cause evolutionary change has demonstrated the power of even weak selective pressures to fix favorable genotypes in populations of moderate-to-large size. Forces such as mutation and random sampling of alleles due to finite population size (genetic drift) are likely to be of minor importance in causing the evolution of 'interesting' characters, although mutation and drift are probably very significant factors in evolution at the level of nucleotide substitutions of little functional signficance. Of course, apart from the most extreme retailers of adaptive Just-So Stories, it is acknowledged that the range of possible variant phenotypes available to a species at any one time is limited by the potentialities of the current developmental system, so that selection is not omnipotent.But a fully explanatory theory of phenotypic evolution requires two kinds of knowledge that we currently lack: knowledge of the spectrum of possible phenotypes that can be produced by the genetic variability available to a given evolving lineage, and an understanding of how fitness is related to phenotype over the duration of the lineage. As Darwin clearly understood, detailed information of the second kind is denied to us by the enormous complexity of the physical and biotic components of the environment that affect the reproductive success of organisms. It is, however, tempting to suppose that the first kind of knowledge can be provided by developmental biology. A predictive theory of the phenotypes which can be realized by mutation would supplant our current reliance on the empirical study of natural genetic variability for determining the nature of the raw material for evolution.There has been a long history of attempts to integrate developmental and evolutionary biology, but the net results of these efforts have, for good reason, had little impact on the thinking of most evolutionary biologists. A major reason for this has been the more or less overt hostility of the proponents of these theories to Darwinian concepts of stepwise adaptive evolution, from Richard GoldSchmidt and D'Arcy Thompson in the 1940% to Pere Alberch, Stephen Gould and Brian Goodwin in the 1980s. This school of thought asserts that selection simply discriminates among a limited set of possibilities thrown up by the 'laws of form' laid down by the fundamental processes of development, which are not themselves the product of selection. Unity of type then does not necessarily reflect common descent: a particular outcome of development could be produced quite independently in different lineages, by fixation of the appropriate mutations.The Origins of Order is an ambitious attempt to provide a detailed theoretical underpinning for the view that the role of selection in adaptive evolution is highly constrained by the possibi...

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