Reconstructing Ancestors: The Lessons from Developmental Evolution

Manfred D. LaubichlerArizona State University and Marine Biological Laboratory, United States of America

Reconstructing ancestral forms has been a major part of analyzing the history of life on earth. For a long time this has been the purview of comparative anatomy, morphology and paleontology. However, for those deep ancestral forms that did not leave any fossil traces embryological data were used as evidence, most prominently by Ernst Haeckel in his Gastraea Theory . In the second half of the 20th century reconstructing concrete ancestral forms has been overshadowed by an operational approach to reconstructing phylogenetic relationships based on molecular and morphological data. More recently, in the context of developmental evolution , the reconstruction of ancestral forms has been revived and developmental data play again a major role. These reconstructed forms, such as Urbilateria represent concrete hypotheses based on a functional understanding of shared elements of the genetic toolkit and of deeply conserved elements of gene regulatory networks. They are also the basis for formulating scenarios of how evolutionary changes in underlying developmental systems can explain major transformations in phenotypic evolution. This talk will sketch the history of attempts to reconstruct deep ancestral forms and explore the role of such reconstructions in transforming evolutionary biology into a causal-mechanistic science.