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.