The philosophy of biology examines the concepts, methods, and explanations of the life sciences. Questions that look technical conceal long-standing philosophical problems: what does it mean to say that the heart is for pumping blood? On what, exactly, does natural selection act: the gene, the organism, the group? Are there species, or only similar individuals that we classify for convenience? Can biology be reduced to chemistry, and can evolution tell us anything about good and evil?

As an autonomous academic discipline, the philosophy of biology consolidated in the second half of the twentieth century, partly because the philosophy of science of the time, centered on physics, set aside the peculiarities of biology. But its questions come from much earlier: from Aristotle, who was also a biologist, and from Kant, who in the Critique of the Power of Judgment dealt with organized beings. This article traces the main axes of the field, with attention to the central authors and works.

1. Aristotelian teleology

For Aristotle, to explain a natural phenomenon is to indicate its four causes (Physics II.3; Metaphysics V.2): material, formal, efficient, and final. The final cause (telos, “end,” “that for the sake of which”) is not an addition to the explanation of living beings but a central part of it: teeth have the form they have in order to cut and grind. Nature (physis) is, for him, an internal principle of motion and rest, and natural beings generally act for the sake of ends without deliberating. See the entries Telos and Physis and the article Physis: Nature and Becoming.

Two aspects matter for the later discussion:

  • Hylomorphism and soul. In On the Soul (II.1), the soul is the form of a natural body that has life potentially; the organism is a unity in which matter and form are distinguished only in analysis. See the entry Hylomorphism.
  • An argument against chance. In Physics II.8 (198b), Aristotle discusses the hypothesis, attributed to Empedocles, that the parts of animals arose by chance and only the viable combinations survived. Aristotle rejects it, holding that natural phenomena occur “always or for the most part” and so cannot be the result of chance. The resemblance to the logic of natural selection is often noted, but the context is different, and Aristotle’s conclusion is the opposite of Darwin’s.

Aristotelian teleology presupposes neither an external planner nor a consciousness: it is a teleology immanent in the form of the living thing. This distinguishes it from modern natural theology.

2. Kant: the organism as a “natural end”

In the Critique of the Power of Judgment (1790, §§ 64–65), Kant describes the organized being as a “natural end” (Naturzweck): a thing in which every part exists for the sake of the others and of the whole, and which is both cause and effect of itself. Kant holds that we cannot understand such beings by mechanical causality alone, but that teleology must be taken as a regulative principle, a necessary way of judging organisms, and not as constitutive knowledge of how nature is in itself. He also stated, in §75, that it would be absurd to hope that some day a “Newton of a blade of grass” might arise, that is, a scientist able to explain the generation of a simple plant by mechanical laws without appeal to ends. This position set the horizon of the problem until Darwin.

3. Darwin and natural selection

Before 1859, the argument from design dominated the explanation of adaptation. William Paley, in Natural Theology (1802), compared the organism to a watch that presupposes a watchmaker. Hume had already criticized the argument in the posthumous Dialogues Concerning Natural Religion (1779) (see the article on Hume), but a positive explanatory alternative was lacking.

Charles Darwin (1809–1882) supplied it in On the Origin of Species (published 24 November 1859). Alfred Russel Wallace (1823–1913) had independently reached the same idea, and a joint communication of Darwin and Wallace had been read at the Linnean Society in 1858. The argument can be reconstructed as follows:

  1. The organisms of a population vary.
  2. Part of that variation is inherited.
  3. More individuals are born than resources allow to survive (the “struggle for existence,” inspired by Malthus).
  4. Individuals with variations that favor survival and reproduction leave, on average, more offspring.
  5. Over many generations the population changes, and complex adaptations and the divergence of lineages appear (descent with modification).

The expression “survival of the fittest” was coined by Herbert Spencer in Principles of Biology (1864) and adopted by Darwin from the fifth edition of the Origin (1869). Darwin considered it a convenient alternative to “natural selection,” but the expression invites error: “fit” refers to differential reproductive success, not to strength or merit.

The philosophical significance was enormous. Natural selection explains apparent design without postulating a design: adaptation results from a blind, cumulative process without a goal. Daniel Dennett, in Darwin’s Dangerous Idea (1995), called the idea a “universal acid” that eats through traditional conceptions (see the profile of Daniel Dennett). In the first half of the twentieth century the theory was combined with Mendelian genetics in the so-called modern synthesis (Fisher, Haldane, Wright, Dobzhansky, Mayr, Simpson), and the discovery of the structure of DNA (1953) opened molecular biology.

4. Teleology, function, and teleonomy

If natural selection dispenses with design, what justifies speaking of functions in biology? We say that the heart has the function of pumping blood, not of making noise. This teleological vocabulary persists in biological discourse and requires analysis.

A first step was the concept of teleonomy, proposed by Colin Pittendrigh (1958) and taken up by Ernst Mayr: a teleonomic system is one whose apparent purposiveness results from an evolutionarily selected program, without conscious purpose. Mayr, for his part, distinguished in “Cause and Effect in Biology” (1961) proximate causes (how the organism works) from ultimate causes (why evolution shaped it thus).

Two families of theories of function stand out:

  • Etiological theories. In “Functions” (Philosophical Review, 1973), Larry Wright proposed that the function of a trait is what explains why it is there: the heart exists because it pumps blood. Ruth Millikan, in Language, Thought, and Other Biological Categories (1984), developed the notion of proper function, tied to the selective history of the trait and of its predecessors. Karen Neander (1991) refined the approach in terms of “selected effects.”
  • Causal-role theories. Robert Cummins, in “Functional Analysis” (Journal of Philosophy, 1975), held that the function of a component is the contribution it makes to a capacity of the system containing it, independently of its history.

Etiological theories explain why we can speak of malfunction: a heart that does not pump still has the function of pumping. But they raise the famous problem of Swampman, an example from Donald Davidson (1987): if lightning by chance formed an exact replica of a person, would its organs have functions, even without a selective history? For causal-role theories the problem does not arise, but they struggle to distinguish functions from accidental useful effects. See the profile of Donald Davidson. The discussion echoes the debate on final causality: see the article on substance in Aristotle, Descartes, and Spinoza.

5. Units of selection: gene, organism, group

On what does natural selection act? Darwin thought mainly of individuals, but in cases such as social insects and human morality he admitted considerations about groups.

5.1 The group and its critique

In the 1960s, V. C. Wynne-Edwards (Animal Dispersion in Relation to Social Behaviour, 1962) argued that behaviors such as reproductive restraint evolved for the good of the group. George C. Williams, in Adaptation and Natural Selection (1966), criticized this “naive group selection,” arguing that selection at higher levels is, as a rule, weak against selection among individuals, and that adaptation should be attributed to the lowest level able to explain it. William Hamilton (1964) presented kin selection: genes can spread by favoring relatives, which explains altruism without appeal to the group.

5.2 The selfish gene

In The Selfish Gene (1976), Richard Dawkins popularized the “gene-centered” view: organisms are “survival machines” of replicators (genes) that persist by copying. In The Extended Phenotype (1982), Dawkins later distinguished the replicator from the “vehicle.” The book was often misunderstood: “selfishness” is a metaphor for the logic of replicative success, not a psychological thesis about human selfishness, and Dawkins held that the kin-selection explanation of altruism is compatible with cooperative behavior.

David Hull (“Individuality and Selection,” 1980) proposed the distinction between replicators and interactors (entities that interact with the environment in a way that favors replication) as a more neutral way of formulating the problem.

5.3 Multilevel selection

Elliott Sober and David Sloan Wilson, in Unto Others (1998), defended multilevel selection: selection can act at once on genes, organisms, and groups, and group selection can explain altruism when variation between groups is sufficient. Defenders of the gene’s-eye view argue that accounting in terms of genes is in principle equivalent (the so-called bookkeeping thesis). Sober, in The Nature of Selection (1984), distinguished selection of objects (what is selected) from selection for properties (what explains the selection). Samir Okasha (Evolution and the Levels of Selection, 2006) offers a critical assessment. The question is philosophical insofar as it depends on what it means to say that something is a cause and not mere bookkeeping.

6. The species problem

The notion of species comes from Aristotle and from the taxonomic tradition of Linnaeus: natural groups defined by fixed essences. An influential narrative, defended by Mayr and Hull, blames “typological essentialism” for a long stagnation in taxonomy; more recent historians debate whether this picture is faithful to the sources. In any case, Darwinian population thinking made the idea of a species essence problematic, since species change and intraspecific variation is the engine of evolution.

6.1 The biological species concept

Ernst Mayr (1904–2005), in Systematics and the Origin of Species (1942), proposed the biological species concept: groups of actually or potentially interbreeding natural populations that are reproductively isolated from other such groups. A species is thus defined by relations of interbreeding, not by similarity. The concept faces limits: it does not apply to asexual organisms, is hard to apply to fossil species, and ignores the frequent hybridization in certain groups.

6.2 Alternatives and pluralism

Among the alternatives are the phylogenetic concept (derived from Willi Hennig’s systematics), which defines species by lineages and ancestry, the ecological concept, and others. Michael Ghiselin (1974) and David Hull (“A Matter of Individuality,” 1978) proposed that species are not classes but individuals (historical entities, spatiotemporally bounded, of which organisms are parts). If so, “Homo sapiens” is like a proper name, not like “gold.” Philip Kitcher (“Species,” 1984) defended a pluralism: different explanatory interests justify different species concepts. The problem connects to the debate on substance and on universals in the philosophical tradition.

7. Reductionism and emergence

Is biology reducible to physics and chemistry? Ernest Nagel (The Structure of Science, 1961) formulated the classical model of theory reduction: a theory is reducible to another if it is derivable from it with the help of “bridge laws.” Kenneth Schaffner applied the model to genetics. David Hull, in Philosophy of Biological Science (1974), argued that the relation between Mendelian and molecular genetics does not fit the model, because there is no simple mapping between the predicates of the two (a Mendelian “gene” can correspond to many molecular sequences, and vice versa). Philip Kitcher, in “1953 and All That” (1984), argued in similar terms that classical genetics was not reduced but integrated. A background argument is multiple realizability (see the profile of Hilary Putnam): the same biological function can be realized by diverse physical substrates.

Historically, opposition to mechanism took the form of vitalism: Hans Driesch postulated, around 1900, an “entelechy” (an Aristotelian term) as a vital principle, and Bergson proposed the élan vital in Creative Evolution (1907). Vitalism was abandoned by biology, in part because it produced no testable predictions. Today the most common position is non-reductive physicalism, which grants that everything biological is composed of physical entities but recognizes emergent properties and proper higher-level explanations. Mayr held a version of organicism, according to which biological systems have properties that cannot be deduced from their isolated parts. The parallel debate in the philosophy of mind is in the article on the mind-body problem. A philosophical version of the question appears in Hans Jonas, for whom the organism, with its metabolism, reveals an incipient form of freedom and inwardness (The Phenomenon of Life, 1966); see also the article on environmental ethics in Hans Jonas.

8. Adaptationism and Gould and Lewontin’s critique

Adaptationism is the tendency to explain organisms’ traits as adaptations shaped by natural selection. In “The Spandrels of San Marco and the Panglossian Paradigm: A Critique of the Adaptationist Programme” (Proceedings of the Royal Society of London B, 205, 1979, pp. 581–598), Stephen Jay Gould and Richard Lewontin attacked the habit of breaking the organism into traits and assigning each an adaptive history, telling plausible “stories” (just-so stories, a reference to Kipling). The central analogy comes from the architecture of St. Mark’s Basilica in Venice: the triangular spaces between arches (the “spandrels”) are a necessary by-product of the architecture and were afterwards decorated; they are not the reason for the design. It has since been observed that the more exact architectural term would be pendentives, but the biological argument does not depend on this. “Panglossian” alludes to Dr. Pangloss in Voltaire’s Candide, who holds that all is for the best in the best of all possible worlds.

The authors pointed to alternatives to selection as explanation: developmental and architectural constraints, genetic drift, by-products (pleiotropy, growth correlation), and the possibility that a structure arose for one reason and was co-opted for another. Gould and Elisabeth Vrba later coined the term exaptation (1982) for traits that now serve a function different from the one for which they were selected.

The critique was not a denial that adaptations exist; it was a refusal of the untested use of selection as a default explanation. Important replies came from Dennett (Darwin’s Dangerous Idea), who held that adaptationist reasoning is a legitimate “reverse engineering” heuristic, and from Mayr, who defended the adaptationist program as a method without denying its limitations. Peter Godfrey-Smith (2001) distinguished empirical adaptationism (selection is the dominant evolutionary force), explanatory adaptationism (adaptation is the central problem of biology), and methodological adaptationism (the adaptive hypothesis is the best research strategy), showing that the discussion had been mixing different theses. The debate touches the philosophy of science: see the article on Popper and Kuhn, since the charge of unfalsifiability aimed at adaptive stories echoes Popper’s criteria (see the profile of Karl Popper).

9. Evolutionary epistemology

Evolutionary epistemology applies biology to the theory of knowledge, in two distinct versions (a distinction due to Michael Bradie, 1986):

  • The evolution of cognitive mechanisms. Our capacities for perception and reasoning are products of natural selection. Konrad Lorenz, in “Kants Lehre vom Apriorischen im Lichte gegenwärtiger Biologie” (1941), suggested that Kant’s a priori categories, which precede the individual’s experience, are a posteriori for the species: forms of intuition fitted to the world over phylogeny. See the article on the a priori and a posteriori and the profile of Kant.
  • The evolution of theories. Donald Campbell (“Evolutionary Epistemology,” 1974) and Karl Popper himself (in Objective Knowledge, 1972) described the growth of scientific knowledge as a process analogous to natural selection: conjectures vary and refuted ones are eliminated.

Recurrent objections: selection favors beliefs useful for survival, not necessarily true ones, and the analogy with natural selection is debatable, since scientific variation is largely directed and not blind. In parallel, W. V. Quine’s “naturalized epistemology” (1969) proposes treating epistemology as a chapter of empirical science.

10. Ethics and evolution

10.1 Spencer, social Darwinism, and the naturalistic fallacy

Herbert Spencer (1820–1903) proposed a synthetic philosophy of evolution that in part preceded Darwin’s: his essay “Progress: Its Law and Cause” dates from 1857. His thought is often called “social Darwinism,” a problematic label, because Spencer was in large measure a Lamarckian and because the term was used more by critics than by defenders. In his view the evolutionary process would lead to ever more complex forms and better-adapted societies, and ethics ought to follow that direction.

G. E. Moore, in Principia Ethica (1903), criticized ethics based on natural properties such as evolution, arguing that “good” is not definable in natural terms, and called “naturalistic fallacy” the error of identifying the good with a natural property (see the entry Naturalistic Fallacy and the profile of G. E. Moore). Distinct, though related, is Hume’s is/ought problem (see the article on Hume): from what is, it does not follow by itself what ought to be. Thomas Huxley, in the lecture Evolution and Ethics (1893), held that the ethical process opposes the cosmic process of struggle and does not follow from it.

10.2 Sociobiology and the origins of morality

Edward O. Wilson, in Sociobiology: The New Synthesis (1975), proposed studying social behavior, human included, in the light of evolutionary biology, and in On Human Nature (1978) extended the perspective. The work drew criticism from scientists such as Gould and Lewontin, who accused it of biological determinism and of exaggerating adaptationism; defenders replied that evolutionary explanation does not imply determinism. Michael Ruse and Wilson (“Moral Philosophy as Applied Science,” 1986) argued that morality is an adaptation and that objective moral “facts” would therefore be an adaptive illusion. Philip Kitcher, in Vaulting Ambition (1985), offered a critical analysis of human sociobiology.

Since then, evolutionary debunking arguments (Richard Joyce, The Evolution of Morality, 2006; Sharon Street, “A Darwinian Dilemma for Realist Theories of Value,” 2006) maintain that if our moral beliefs were shaped by selective pressures indifferent to moral truth, moral realism faces a problem. Realist replies contest the premise or propose that selection favored the detection of moral facts. In another direction, Peter Singer (The Expanding Circle, 1981) uses the evolutionary origin of cooperation to argue that reason can widen the circle of moral concern (see the profile of Peter Singer and the article on animal welfare); and the moral psychology of Joshua Greene investigates the evolutionary basis of moral intuitions. For the general context, see the articles on normative ethics (utilitarianism) and bioethics.

11. Contemporary philosophy of biology

Three names often associated with the consolidation of the field deserve mention.

  • David Hull (1935–2010), with Philosophy of Biological Science (1974), “A Matter of Individuality” (1978), and Science as a Process (1988), dealt with the nature of species, reductionism, and the evolution of scientific knowledge as a process of selection among scientists.
  • Michael Ruse (b. 1940), with The Darwinian Revolution (1979) and Taking Darwin Seriously (1986), wrote on the history of Darwinism and its relation to morality, and testified in McLean v. Arkansas (1981–82) against the teaching of creationism, a case that reopened the debate on the demarcation criterion between science and non-science (Larry Laudan later criticized the criteria then used).
  • Philip Kitcher (b. 1947), with Abusing Science (1982, a critique of creationism), Vaulting Ambition (1985), and Living with Darwin (2007), combined philosophy of science, of biology, and ethics.

Among ongoing discussions are evolutionary developmental biology (evo-devo), niche construction, epigenetics, and the debate over whether evolutionary theory needs an “extended synthesis” (Laland and colleagues, Nature, 2014), a controversy in which defenders of the standard synthesis hold that the new phenomena are already accommodated by the existing framework. The philosophy of molecular biology and systems biology, the notion of genetic information, and the questions opened by gene editing (CRISPR), which link the philosophy of biology to bioethics, have also gained ground.

12. Closing remarks

The philosophy of biology shows how classical problems reappear in a new form. Aristotle’s final cause resurfaces in the functional vocabulary of biology, reinterpreted in terms of selective history. The Kantian question of the organism as a totality is reflected in the debate over reductionism and emergence. The problem of universals and essence reappears in the debate over species, and the problem of the foundation of knowledge in epistemological naturalism. At the same time, the question of what evolution tells us about value and duty remains in dispute, and the answers the literature offers, from Spencer to Moore, from Wilson to Singer, do not converge.

References

ARISTOTLE. Physics; Parts of Animals; On the Soul; Metaphysics.

CAMPBELL, Donald T. “Evolutionary Epistemology.” In: SCHILPP, P. A. (ed.). The Philosophy of Karl Popper. La Salle: Open Court, 1974.

DARWIN, Charles. On the Origin of Species. London: John Murray, 1859.

DAWKINS, Richard. The Selfish Gene. Oxford: Oxford University Press, 1976.

DENNETT, Daniel C. Darwin’s Dangerous Idea. New York: Simon & Schuster, 1995.

GODFREY-SMITH, Peter. “Three Kinds of Adaptationism.” In: ORZACK, S. H.; SOBER, E. (eds.). Adaptationism and Optimality. Cambridge: Cambridge University Press, 2001.

GOULD, Stephen Jay; LEWONTIN, Richard C. “The Spandrels of San Marco and the Panglossian Paradigm: A Critique of the Adaptationist Programme.” Proceedings of the Royal Society of London B, 205, 1979, pp. 581–598.

HULL, David L. “A Matter of Individuality.” Philosophy of Science, 45, 1978.

HULL, David L. Philosophy of Biological Science. Englewood Cliffs: Prentice-Hall, 1974.

KANT, Immanuel. Critique of the Power of Judgment, 1790.

KITCHER, Philip. Vaulting Ambition: Sociobiology and the Quest for Human Nature. Cambridge, MA: MIT Press, 1985.

MAYR, Ernst. Systematics and the Origin of Species. New York: Columbia University Press, 1942.

MILLIKAN, Ruth G. Language, Thought, and Other Biological Categories. Cambridge, MA: MIT Press, 1984.

MOORE, G. E. Principia Ethica. Cambridge: Cambridge University Press, 1903.

OKASHA, Samir. Evolution and the Levels of Selection. Oxford: Oxford University Press, 2006.

SOBER, Elliott; WILSON, David Sloan. Unto Others: The Evolution and Psychology of Unselfish Behavior. Cambridge, MA: Harvard University Press, 1998.

WILSON, Edward O. Sociobiology: The New Synthesis. Cambridge, MA: Harvard University Press, 1975.

WRIGHT, Larry. “Functions.” Philosophical Review, 82, 1973.

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