The continuity of microevolution and macroevolution

A persistent debate in evolutionary biology is one over the continuity of microevolution and macroevolution – whether macroevolutionary trends are governed by the principles of microevolution. The opposition of evolutionary trends over different time scales is taken as evidence that selection is uncoupled over these scales. I argue that the paradox inferred by trend opposition is eliminated by a hierarchical application of the ‘geometric‐mean fitness’ principle, a principle that has been invoked only within the limited context of microevolution in response to environmental variance. This principle implies the elimination of well adapted genotypes – even those with the highest arithmetic mean fitness over a shorter time scale. Contingent on premises concerning the temporal structure of environmental variance, selectivity of extinction, and clade‐level heritability, the evolutionary outcome of major environmental change may be viewed as identical in principle to the outcome of minor environmental fluctuations over the short‐term. Trend reversals are thus recognized as a fundamental property of selection operating at any phylogenetic level that occur in response to event severities of any magnitude over all time scales. This ‘bet‐hedging’ perspective differs from others in that a specified, single hierarchical selective process is proposed to explain observed hierarchical patterns of extinction.