Ushering in the new ‘modern synthesis’

Abstract

View Large Image | Download PowerPoint SlideWhen Darwin proposed the idea of natural selection during the 19th century, the major limitation to his theory was how to explain the notion of ‘heritable variation’. During the 20th century, one half of this problem (the explanation of the inheritance of genetic variation) was resolved through the work of Fisher, Haldane, and Wright, which culminated with the ‘modern synthesis’. The other half of the problem (how genetic variation gives rise to morphological differences between species) has only begun to be addressed more recently through advances in the field of evolutionary developmental biology, or evo-devo, and this will undoubtedly be a major contribution to evolutionary theory, ushering in a ‘new modern synthesis’ for the 21st century.In this light, Wallace Arthur's Evolution: A Developmental Approach looks forward to this new synthesis, covering the major themes of evo-devo in a brief and focussed text. The book begins with a rather lengthy introductory section covering the fundamentals of genetics, molecular, cell, and developmental biology (a necessary evil for any introductory development text), and this is followed by two main sections that the author has entitled ‘Developmental Repatterning’ and ‘The Direction of Evolution’. The first of these deals with the different ways in which development can evolve, providing examples of heterochrony, heterotopy, heterometry, and heterotypy and how these different forms of change are integrated. The second section deals with the mechanisms that steer the course of evolution, including co-adaptation, exaptation, developmental bias and constraint, plasticity, and the evolution of complexity. The book ends with a short section that offers a summary of the main conclusions and prospects for the future of evo-devo.In the preface to Evolution: A Developmental Approach, Arthur explains that he has written the text for students taking a course in evolution at university or college, yet it is not clearly focussed on this audience. It is unquestionably an introductory text: it is too technical for popular science, but not comprehensive or detailed enough for an upper division or graduate-level course, despite the references provided in the bibliography. The book is written in a casual, conversational style (for which it has been praised) and, although this will no doubt be appealing to an undergraduate audience, it is less appropriate for a more advanced one. By contrast, the text does more than simply recount the various experiments and conclusions that have formed the foundations of the evo-devo field, as a typical introductory text would. Arthur takes a step back from the data and tries to reassess the field as a whole, redefining terms, proposing new ones, and challenging some of the long-standing dogmas in the field. This is a very thought-provoking perspective; however, because it has not been vetted out in the wider scientific community, it is questionable whether it is the best approach for a naive audience. One of the strengths of the text is its candid approach to the limitations to the interpretation of scientific experiments, which is important in a field where the temptation to propose ‘just-so’ stories is all too strong. However, although this is important for developing critical thinking in more advanced students, it is so prevalent in the book that one is sometimes left wondering whether definitive conclusions can be made from evo-devo studies. This may put off the young biology students at whom the book is aimed. It is also not clear how this text would fit into a typical undergraduate curriculum. Although it is an excellent overview of evo-devo, Arthur has purposely left out most of the basic material on evolutionary theory and focussed his text on developmental evolution. As forward thinking as this may be, a typical undergraduate course will still need to cover classical evolutionary theory and, thus, this text would be, at best, a companion alongside a more conventional evolution text.These issues aside, the text is a first step in the right direction and is looking forward to the new synthesis that developmental biology is going to bring to evolutionary theory during the 21st century.