Reinventing the Organism: Evolvability and Homology in Post-Dahlem Evolutionary Biology

Abstract

The 1981 Dahlem conference marked a turning point in the history of evolutionary biology, from a predominantly gene-centric to a pluralistic view of evolutionary causation. In particular, the ideas exchanged at this meeting were the seed for an organismic turn, in which the systems properties of organisms assumed conceptual centrality. This point is illustrated with two examples: evolvability and homology. Evolvability, i.e. the ability to improve in fitness by random mutation and selection, requires certain properties of the genotype–phenotype map. These properties, like limited pleiotropy and modularity, are consequences of the developmental organization of organisms. Hence, the structure of organisms gains conceptual centrality because its properties are essential for understanding adaptation by mutation and natural selection. Homology is another concept that (re)gained prominence after the 1981 Dahlem conference. It is argued that homology describes a pattern of phenotype evolution that reflects and is explained by the developmental structure of organisms, again demonstrating the centrality of the organism concept in post-Dahlem evolutionary biology.