More on punctuated equilibrium

Abstract. The long-controversial theory of punctuated equilibrium (PE) asserts that speciation causes rapid evolution against a backdrop of stasis. PE is currently undergoing a resurgence driven by new developments in statistical methods. However, we argue that PE is actually a tangle of four unnecessarily conflated questions: (i) is evolution gradualistic or pulsed? (ii) does trait evolution occur mainly at speciation or within a lineage? (iii) are changes at speciation adaptive or neutral? and (iv) how important is species selection in shaping patterns of diversity? We discuss progress towards answering these four questions but argue that combining these conceptually distinct ideas under the single framework of PE is distracting and confusing, and more likely to hinder progress than to spur it.