phyletic gradualism

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Editorial synthesis · provisional

Definition

Phyletic gradualism is the model of evolutionary change as comparatively steady, slow divergence within lineages. RB1 contrasts it with punctuated equilibrium’s long morphological stasis and relatively rapid speciation-associated change. The contrast concerns tempo and pattern rather than whether descent with modification occurs; the corpus preserves continuing disagreement and allows gradual change in some contexts instead of declaring every evolutionary process abrupt or the gradualist model universally refuted.

Explanation

The figure caption explicitly contrasts slow divergence with a punctuated pattern, while the accompanying variation discussion identifies Gould and Eldredge’s challenge to the assumption of uniformly gradual change. The proposed definition records the model without confusing gradualism with a denial that lineages can branch or with an independent origin of each species.

RB1’s later assessment retains a qualification: some biologists argue gradual change is common in other settings, and the author’s point need not depend on strict acceptance of punctuated equilibrium. Its native fossil references supply the provenance of the debate rather than a new statistical comparison performed here.

AB likewise uses an uneven evolutionary trajectory without presenting all novelty as an instantaneous leap. RB2’s layered temporal account allows processes to accumulate on different timescales before a visible change. These passages preserve distinctions among observed tempo, population mechanisms and the broader philosophical claim that new organization arises.

Scope and attribution

Preserve the model contrast and the text’s explicit continuing-context qualification.

RB1 — The Real Book, Volume I: The Possible Is Real

The gradualist model is contrasted with punctuated patterns but not universally declared obsolete.

Occurrence locators: 148, 149, 151, 154, 170, 171, 172.

Background used in the editorial explanation

Named theories and mechanisms are distinguished from neighboring background, homonyms and the author’s own synthesis. Reproduced AI passages retain their separate voice.