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David Hull (1935–2010)

Hull applied Darwinian selection theory to the evolution of science itself. Science as a Process: An Evolutionary Account of the Social and Conceptual Development of Science (1988) argued that scientific change is genuinely selective — that theories, methods, and research programmes compete, replicate, and are differentially retained in a process structurally analogous to biological evolution. The claim is not a loose metaphor: Hull developed the replicator-interactor framework (generalising Dawkins’ replicator-vehicle distinction) and showed that it applies to the units of scientific change as rigorously as to biological populations. He was also a leading philosopher of biology in his own right — his species-as-individuals thesis (that species are not natural kinds but historical individuals) reshaped the metaphysics of biology and connected the philosophy of biology to the philosophy of science in ways that remain productive.

Life

Born 15 June 1935 in Evanston, Illinois. Undergraduate at Illinois Wesleyan University. PhD in the history and philosophy of science at Indiana University (1964), under Norwood Russell Hanson. Taught at the University of Wisconsin-Milwaukee (1964–84), then Northwestern University (1984–2010). Founding member of the International Society for the History, Philosophy, and Social Studies of Biology (ISHPSSB), the professional society that institutionalised the philosophy of biology as a field.

Hull was a participant-observer in the scientific communities he studied. Science as a Process was based on years of fieldwork — attending conferences, reading correspondence, interviewing scientists, tracking the fate of ideas through citation networks — within the systematics community, where the cladistics revolution of the 1970s and 1980s provided a live case study of scientific change. The book’s empirical detail is unusual for a philosophical work and is part of what gives its arguments force.

Died 11 August 2010 in Evanston, Illinois.

Science as a Process

Science as a Process (1988) argues that the conceptual development of science is a selection process in the same structural sense as biological evolution. The argument has three components:

The replicator-interactor framework. Hull generalises Dawkins’ replicator-vehicle distinction into a more abstract framework. A replicator is any entity whose structure is passed on in successive replications (genes in biology, ideas or memes in culture, theoretical claims in science). An interactor is any entity that interacts as a cohesive whole with its environment in a way that causes differential replication (organisms in biology, scientists or research groups in science). Selection is the process in which the differential success of interactors causes the differential replication of replicators. The framework is substrate-neutral: it applies wherever the replicator-interactor structure is instantiated.

The case study. Hull documents the cladistics revolution in systematics — the displacement of traditional (phenetic and evolutionary) classification by Willi Hennig’s cladistic method, which classifies organisms strictly by shared derived characters (synapomorphies) rather than by overall similarity. Hull traces how the idea propagated through particular scientists, institutions, journals, and controversies — showing that the social process (who trained whom, who controlled which journals, which personalities clashed) and the conceptual process (which method produces better classifications and why) are not separate but intertwined. Scientific change, on Hull’s account, is driven by ambition, credit, and institutional competition as much as by evidence and argument — but the social and the epistemic are not opposed; they are the same selection process viewed from different angles.

The credit economy. Scientists are motivated by credit — recognition, citation, influence, the desire to have their ideas adopted. This is not a cynical observation but a structural one: the credit economy provides the incentive structure that makes science work as a selection process. Scientists who produce ideas that are taken up by others receive credit; scientists whose ideas are ignored do not. The system is imperfect (credit is often misallocated, priority disputes are common, institutional power distorts the process), but it functions as the fitness landscape of science: ideas that are “used” — cited, tested, extended, applied — persist; ideas that are not used are pruned.

The species-as-individuals thesis

Hull’s other major contribution, developed in parallel with Michael Ghiselin: species are not natural kinds (classes defined by shared properties) but historical individuals (spatiotemporally bounded, particular entities). A species is not defined by a set of properties that all its members share — there are no such properties, because variation is the norm and no trait is universal within a species. A species is defined by its historical continuity — its lineage, its ancestry, its cohesion through gene flow and common descent.

The thesis has metaphysical consequences. Natural kinds support laws: “All gold melts at 1064°C” is a law because “gold” names a natural kind. If species are individuals, not kinds, then there are no laws about particular species — no law that “all swans are white” or “all humans are rational.” Generalisations about species are empirical summaries, not laws. This connects the philosophy of biology to the philosophy of science: if the basic units of biological theory are individuals rather than kinds, then biology has a different logical structure from physics — a point Hull pressed throughout his career.

Where Hull stops

The selection-theory-of-science analogy has been pressed on its disanalogies. In biological evolution, replication is high-fidelity (DNA copying has error rates of roughly one per billion base pairs per replication); in science, the “replication” of an idea involves transformation — scientists modify, reinterpret, and extend ideas in transmission. Dan Sperber argued that cultural transmission is not replication in the genetic sense, and the objection applies to scientific transmission as well. Whether the transformations are noise (imperfect replication) or the main event (creative modification is how science works) determines whether the selection analogy illuminates or obscures. Hull acknowledged the disanalogy but argued that the replicator-interactor framework is abstract enough to accommodate transformative replication.

The credit-economy model captures the incentive structure of science but not the full range of epistemic forces. Not all scientific change is driven by competition for credit: some ideas persist because they are true (or closer to true than alternatives), and the credit economy is the mechanism through which truth-tracking happens, not an independent force. Hull’s account risks making science sound more like a market than an inquiry — a concern that Philip Kitcher and others have raised. Whether the selection model is a complete account of scientific change or a partial account that captures the competitive dynamics while missing the epistemic ones is debated.

The species-as-individuals thesis is widely accepted but has consequences Hull did not fully develop. If species are individuals, then the evolutionary process creates new individuals (speciation) and destroys existing ones (extinction) — but the mechanism of individuation (what holds a species together as a cohesive entity) is not fully specified. Gene flow, interbreeding, and common descent are the standard answers for sexual species; for asexual species, the question of what makes a species a cohesive individual remains open. The thesis clarifies the ontology but defers the mechanism.

Key works

See also: Dawkins · Sober · Kuhn · Darwinism