Evolution and Development IV: Developmental Genetics

Evolution has resulted in organisms that develop. For a long time the processes of evolution and development have been theoretically and empirically largely independent. This was epitomized by the gene selectionist view of evolution, which rendered the process of development largely epiphenominal to the evolutionary business of evolving the genome. However, there is now a growing awareness that an understanding of development is essential to a complete understanding of evolution and vice versa. This session addresses what this 'developmental synthesis' may contribute and some difficulties that must be overcome for its success in four sessions:

Organized by: Kelly Smith & Roger Sansom

Marion Blute, University of Toronto
"Origins and the Evo-Devo Problem"

One of the oldest but currently less popular versions of the "evo-devo" problem puts it in terms of origins. "What came first, the chicken or the egg?" In theory, origins may be singular or multiple and may be in a smaller, less complex juvenile or in a larger, more complex mature form(s). The 'multiple and mature' answer is implied by the textbook evolutionary perspective which begins its story of generation with a population of mature adults reproducing. Evolution came first and development must have evolved. The 'singular and juvenile' answer is implied by the textbook developmental perspective which begins its story of generation with a single (typical or average) individual growing and developing, including developing reproductive cells. Development came first and evolution must have developed. Is what is sought therefore an evolutionary theory of development or a developmental theory of evolution or somehow both? Evolutionary ecology may contain some general principles relevant to this question. [ Full Paper ]

Richard M. Burian, Virginia Tech
"Developmental Genes, Developmental Modules and Changed Perspectives on the Evolution of Organisms"

Recent work in developmental biology has found highly specific hierarchically organized regulatory modules controlling the identities of various segments and parts of metazoan bodies and, apparently, regulating some of the processes involved in constructing them. The so-called developmental genes (and their products) that play key roles in these regulatory processes show remarkable invariance in evolution. Indeed, in general developmental genes were discovered not because of the existence of different alleles in nature (this is how classical Mendelian genes were found) but because of the deficits that occur when they are mutated. And once a few of them were found, many more were located in widely divergent organisms because of their highly conserved (sequence) similarities to the original, hard-won genes, that is by fishing out sequences rather than by functional analysis. As is now widely known, these sequence similarities generally preserve functional similarities; some developmental genes can perform parallel functions after being transplanted from organisms as widely separated as drosophila and mice. Since these functions include specification of segment or part identity and triggering of organogenesis, these findings suggest new understanding of homologies, of mosaic evolution, of the processes that control segment identity, and of much more. In this paper I will explore some of the implications of these findings for the principles of construction of metazoan bodies, the level at which evolutionary processes occur, and the role of biotechnology in evolutionary theorizing.

Kelly Smith, Clemson University

Commentary and Questions

Scheduled Discussion