Phyletic Gradualism

Phyletic gradualism is the classical Darwinian view that evolution proceeds by the slow, steady accumulation of small changes within a single lineage over geological time, producing a smooth transformation of species into descendant species without branching. This model assumes that the fossil record's gaps are merely artifacts of incomplete preservation, and that given enough data, every transition would appear continuous. The problem is not that gradualism is impossible — it is demonstrably rare in the fossil record, and population genetic models suggest that large, stable populations resist the directional change gradualism requires. Punctuated equilibrium won the empirical argument not by proving gradualism false but by showing that stasis, not change, is the dominant pattern — and that when change occurs, it is concentrated at speciation events (see cladogenesis) rather than distributed uniformly through time.

The persistence of gradualism as a default assumption in popular culture says more about our narrative preferences than about biology. We prefer stories of continuous improvement to stories of frozen form punctuated by crisis.