Background/Question/Methods Understanding the origin of diversity is a fundamental problem in biology. Traditional evolutionary theory predicts uniformity: natural selection, acting on organisms under given environmental conditions and developmental constraints, produces a unique, optimally adapted phenotype. According to this view, different types only come about through a change in conditions over space or time. In particular, the process of diversification, that is, the split of an ancestral population into distinct descendent lineages, is a by-product of geographical separation. This traditional view misses out on the important perspective that diversification itself can be an adaptive process that is driven by ecological interactions.

Results/Conclusions In this talk I will first review basic theoretical concepts illustrating that diversification as a response to ecological interactions is a plausible evolutionary process. I will then describe ongoing efforts to test the theory of adaptive diversification in evolving Escherichia coli populations, which provide promising experimental model systems for studying adaptive diversification at the genetic, physiological and ecological level.