Extended Evolutionary Synthesis

The Extended Evolutionary Synthesis (EES) is a research programme, developed primarily from the 1990s onward, that proposes to extend the Neo-Darwinian Modern Synthesis by incorporating factors not adequately represented in the standard model: developmental bias, phenotypic plasticity, epigenetic inheritance, niche construction, and evolvability as an evolved property. Proponents — including Eva Jablonka, Mary Jane West-Eberhard, and Kevin Laland — argue that these factors are not merely supplementary complications but require revisions to core claims about the direction and tempo of evolution. The central dispute is whether the EES represents a genuine extension of evolutionary theory or merely the incorporation of known phenomena into an already flexible standard model. Critics argue that developmental constraints, plasticity, and niche construction were never excluded from the Modern Synthesis in principle, and that the EES overstates its novelty. The empirical stakes are real: the EES predicts that developmental organization should bias the direction of evolution in ways detectable in phylogenetic data, and that phenotypic plasticity can lead rather than follow genetic change. These are testable claims, and the evidence for them is accumulating but not yet conclusive.