What Is the Promise of Developmental Evolution? III. The Crucible of Developmental Evolution GU ¨ NTER P. WAGNER n1 and HANS C.E. LARSSON 2 1 Department of Ecology and Evolutionary Biology, Yale University, New Haven, Connecticut 2 Redpath Museum, McGill University, Montreal, Quebec, Canada Evolutionary developmental biology has the institutional hallmarks of a successful scientific discipline. There are many faculty positions offered at the best universities, three international journals are dedicated to the subject 1 , an increas- ing number of textbooks introducing the unin- itiated to the field (Carroll et al., 2001; Davidson, 2001; Wilkins, 2002), and even a special National Science Foundation panel to support research in the area. History, however, shows that enthusiasm and institutional successes do not guarantee the continued scientific leadership of a discipline (Nyhart, ’95). Ultimately the success of a disci- pline depends on its ability to deliver on the promise the practitioners saw when the field was introduced. A minimal requirement for delivering on such promise is a common understanding among the practitioners of a discipline on what types of data count as evidence and how such evidence distinguishes between correct and incor- rect hypotheses. While developmental evolution (devo-evo) has made great progress over recent years, as witnessed in the above cited textbooks, the standards of evidence are handled quite variably in different parts of the field. This is not surprising given the number of independent disciplines contributing to devo-evo, each with its own research tradition and standards of evidence. The ultimate success of devo-evo, however, will depend on a synthesis of these disparate metho- dological standards. A historical example that tells a cautionary tale for devo-evo is that of evolutionary morphology. In the second half of the 19th century, evolutionary morphology was a fast growing, successful new discipline similar to devo-evo today. It was a synthesis of comparative anatomy and morphology with evolutionary Darwinian thinking. The most prominent leaders of evolutionary morphology were the invertebrate biologist, Ernst Haeckel (1834–1919) and the vertebrate biologist, Carl Gegenbaur (1826–1903). Indeed, it was some of the very questions formulated by those research- ers, more than 100 years ago, that have re- emerged in the new devo-evo synthesis; for example, the origin of vertebrates, the fin-limb transition, and others (Hall, ’92; Raff, ’96). By the end of the 19th century, however, evolutionary morphology had lost its ability to recruit a critical mass of young scientists and thus lost much of its momentum. Lynn Nyhart has argued that the reason for the loss of evolutionary morphology’s prominent status was, in part, the inability of its practitioners to agree on standards of evidence to evaluate the veracity of evolutionary scenarios (Nyhart, ’95; Nyhart, 2002). Specifically, there were no methods to evaluate the primacy of anatomical versus developmental data for any particular evolutionary hypothesis, leaving the researcher to rely only on personal bias. Examples are the controversies over the origin of paired appendages in vertebrates (Nyhart, ’95) and the role of segmentation of the vertebrate head (Kuratani, 2003; Mitgutsch, 2003). This led to heated personal debates that ultimately convinced the younger generation that the field was not very promising (Nyhart, 1995; Nyhart, 2002). Devo-evo is starting from a stronger position than evolutionary morphology. Nowadays the study of phylogenetic relationships and character evolution are somewhat separated tasks. Evolu- tionary morphology had the enormous task of resolving both simultaneously while including hypotheses as to the process of evolution. In n Correspondence to: Gu ¨nter P. Wagner, Yale University, PO Box 208103, New Haven, CT 06520-8103. E-mail: gunter.wagner@yale.edu Received 27 August 2003; Accepted 23 September 2003 Published online in Wiley InterScience (www.interscience.wiley. com). DOI: 10.1002/jez.b.00041 1 ‘‘Evolution and Development,’’ ‘‘Genes, Development and Evolu- tion,’’ and ‘‘JEZ-Part B: Molecular and Developmental Evolution.’’ r 2003 WILEY-LISS, INC. JOURNAL OF EXPERIMENTAL ZOOLOGY 300B:1–4 (2003)