Abstract

The Extended Evolutionary Synthesis (EES) has been presented as an expansion of the Modern Synthesis (MS). A common and parsimonious view maintains that MS's quantitative evolutionary biology remains both valid and central within the EES, insofar as the EES primarily introduces a more elaborate qualitative research agenda. This article examines the relationship between qualitative and quantitative approaches in the EES debate and argues for a more complex view of how the EES relates to the MS. Its guiding question is whether quantitative evolutionary biology itself might call for an EES. Although no specific answer is supported, the article analyzes the significance of this question and surveys the principal positions in the current literature. Two aims structure the discussion. First, by providing a detailed literature review, I show that, over the past two decades, quantitative research programs have increasingly contributed to modeling the phenomena at the core of the EES. The rationale for the EES is not confined to qualitative considerations; a growing body of work now (re)interprets population-level dynamics through the EES lens. Second, I present the problem of models: Is the mathematical framework of the MS sufficient to account for the phenomena emphasized by the EES, or must these models be extended? I identify and discuss four main positions: (1) strong accretionism-standard quantitative 1 evolutionary biology is enough; (2) mild accretionism-the continuous historical expansion implies that current extensions do not constitute a substantive theoretical shift; (3) mild radicalism-population models require EES assumptions and novel applications; and (4) strong radicalism-some biological phenomena demand genuine modifications to the existing modeling framework.