Evolution and the genetic analysis of populations: 1950-2000

Population genetics had played a key role in the fusion of Mendelian genetics acid Darwinian natural selection into the Synthetic Theory of Evolution. The realization that all basic processes of evolution occur in or among populations suggested that evolutionary processes at all levels could be extrapolated from observations on living populations. In plants, an active tradition in ecological genetics had prepared the ground for the Synthesis, and the new initiative of "biosystematics" made full use of experimental and analytical techniques for systematics, especially at the level of species. This development got caught up in the "hardening of the Synthesis", the defensive persistence on a simplified core theory in the face of challenges from known facts and new discoveries, especially in molecular genetics. Enzyme electrophoresis was the First molecular method to be introduced into population biology. The new results revealed unexpectedly high levels of variation within populations and precipitated discussion about the selective neutrality of protein polymorphisms. This discussion distracted attention from the population genetic basis of organismic evolution. Together with the widespread adoption of molecular marker methods at the expense of other approaches, population genetics was in danger of losing its central relevance and its variety of experimental approaches. Since the end of the 1970s, calls for new initiatives have drawn attention to me importance of historical contingency in evolution, especially in the form of developmental constraints. A population genetic application of these ideas initially faced immense technical problems. A succession of new molecular marker systems suitable for the genetic analysis of populations added new resolving power, but introduced new problems with the inference of processes from basically static and descriptive data. Only very recently, methods have advanced to the point that molecular markers can help in the experimental analysis of morphological and physiological evolution. The coming challenge will be to adapt results from detailed analyses of individual plants to broadly comparative population genetic studies. The accumulated new insights of the last 50 years show that the pervasive influence of historical contingency has non-trivial consequences for evolutionary biology and taxonomy. These are strikingly exemplified by a completely changed picture of genome structure and evolution. The time seems to be right for a paradigm shift in evolutionary biology.