Statistical Mechanics of Modularity and Horizontal Gene Transfer

Biological structure organizes over evolutionary timescales. This review discusses the spontaneous emergence of hierarchical structure in biology as a result of environmental change. A body of theoretical and experimental work on evolutionary dynamics is reviewed, and a theory for these results based on a principle of least action is discussed. The structure that has emerged in biology is complementary to a type of evolutionary dynamics known as horizontal gene transfer. How horizontal gene transfer ameliorates the difficulty that finite populations would otherwise have to evolve on rugged fitness landscapes is also discussed.