Thomas Kuhn had little to say about scientific change in biological science, and biologists are ambivalent about how applicable his framework is for their disciplines. We apply Kuhn’s account of paradigm change to evolutionary microbiology, where key Darwinian tenets are being challenged by two decades of findings from molecular phylogenetics. The chief culprit is lateral gene transfer, which undermines the role of vertical descent and the representation of evolutionary history as a tree of life. To assess Kuhn’s relevance to this (...) controversy, we add a social analysis of the scientists involved to the historical and philosophical debates. We conclude that while Kuhn’s account may capture aspects of the pattern of an episode of scientific change, he has little to say about how the process of generating new understandings is occurring in evolutionary microbiology. Once Kuhn’s application is limited to that of an initial investigative probe into how scientific problem-solving occurs, his disciplinary scope becomes broader. (shrink)

Mutation and lateral transfer are two categories of processes generating genetic diversity in prokaryotic genomes. Their relative importance varies between lineages, yet both are complementary rather than independent, separable evolutionary forces. The replication process inevitably merges together their effects on the genome. We develop the concept of “open lineages” to characterize evolutionary lineages that over time accumulate more changes in their genomes by lateral transfer than by mutation. They contrast with “closed lineages,” in which most of the changes are caused (...) by mutation. Open and closed lineages are interspersed along the branches of any tree of prokaryotes. This patchy distribution conflicts with the basic assumptions of traditional phylogenetic approaches. As a result, a tree representation including both open and closed lineages is a misrepresentation. The evolution of all prokaryotic lineages cannot be studied under a single model unless new phylogenetic approaches that are more pluralistic about lineage evolution are designed. (shrink)