The idea that the development of individuals is a progression through adult ancestral forms, epitomised in the saying "ontogeny recapitulates phylogeny", has played an important part in the history of biology. Since the rejection of recapitulationist ideas in the early part of this century, however, the study of links between development and evolution has been relatively neglected. Ontogeny and Phylogeny is divided into two roughly equal sections. The first is an outline of the history of the idea of recapitulation and the second presents the author's own ideas on the relationship between evolution and development.
The first part begins with a brief look at prefigurations of the idea of recapitulation in Greek philosophy. It then traces the history of recapitulationist ideas from preformationist beginnings with Bonnet, through the heyday of the Naturphilosophie school, to their apex with the formulation of a recapitulationary theory by Haeckel. It describes the changes to recapitulationary theories with the spread of evolutionary theories and their final demise with the rise of experimental embryology and the rediscovery of Mendelian genetics. The historical narrative is broken by a chapter on the pervasiveness of the idea of recapitulation outside biology, in such diverse areas as racism, child development, education, criminal anthropology and psychoanalysis.
As always, Gould has a good feel for the historical background of the science, and rejects retrospective reinterpretations in the light of the modern synthesis. He couples a grasp of the broad sweep of the history of ideas with an eye for the finest detail.
In the second part Gould presents his own ideas on heterochrony (evolutionary changes in the timing of development), presenting a unified view of neoteny, recapitulation, paedogenesis, retardation, progenesis, etc. His basic idea is that all heterochrony is a result of acceleration or retardation of different developmental processes (growth, sexual maturation, morphological changes, etc.), and that it is these processes that are important rather than their results.
He then discusses the evolutionary and ecological significance of heterochrony. He stresses the need to consider the immediate advantages to organisms of developmental changes, as well as long term and retrospective macroevolutionary explanations. He goes through in some detail examples of progenesis and neoteny in insects and amphibians, relating them to different ecological strategies. (In insects r strategies are commonly associated with progenesis and K strategies with neoteny, though there are exceptions.)
The final chapter discusses the importance of neoteny in human evolution. Early "fetalisation" theories were rejected because they were built on flawed theories of evolution, but their basic ideas are argued to have been correct. The evidence overwhelmingly suggests that retardation was one of the most important processes involved in the origin of homo sapiens.