Part IX: Philosophy of Biology
Chapters 25–27: Natural Selection & Teleology, The Species Problem, and Reductionism vs Emergence
Biology occupies a peculiar position in the philosophy of science. For much of the twentieth century, philosophy of science was effectively philosophy of physics — the examples were drawn from mechanics, thermodynamics, and quantum theory, and the models of explanation, law, and reduction were tailored to the physical sciences. Yet biology raises distinctive philosophical problems that cannot be shoehorned into frameworks designed for physics. The organisms that populate the biological world are products of a historical process — evolution by natural selection — and this gives biological explanation a narrative, historical character that has no analogue in fundamental physics.
Part IX of this course explores three central problems in the philosophy of biology. First, we examine natural selection and teleology: Darwin’s theory appears to eliminate purpose from nature, yet biologists routinely speak of the “function” of the heart or the “purpose” of camouflage. How do we reconcile mechanistic explanation with the apparently teleological character of biological phenomena? Second, we confront the species problem: the seemingly simple question “What is a species?” has generated a bewildering proliferation of competing definitions, each capturing a different aspect of biological reality. Third, we address the debate over reductionism and emergence: can biology be reduced to chemistry and physics, or do biological phenomena exhibit genuine emergence that resists reduction?
These questions are not merely academic curiosities. They bear on practical matters of conservation policy, medical research, and our understanding of what it means to be a living organism in a world shaped by billions of years of evolution. The philosophy of biology has emerged since the 1970s as one of the most vibrant subfields of philosophy of science, attracting both philosophers and biologists to its central debates.
The Distinctiveness of Biology
Ernst Mayr, one of the twentieth century’s greatest evolutionary biologists, argued forcefully that biology is an autonomous science, irreducible to physics. In The Growth of Biological Thought(1982), Mayr identified several features that distinguish biology from the physical sciences:
- •Historical contingency: Biological phenomena are products of evolutionary history. Unlike the laws of physics, which hold universally and atemporally, biological generalizations are historically contingent. The genetic code is universal on Earth, but this is an accident of history, not a law of nature.
- •Population thinking: Physics deals with types; biology deals with populations of unique individuals. No two organisms are identical. This “population thinking,” which replaced the essentialist “typological thinking” of pre-Darwinian biology, is one of Darwin’s most profound conceptual innovations.
- •Teleology: Biological systems exhibit goal-directedness and functional organization. The heart pumps blood; the eye sees. This teleological character has no counterpart in physics and has generated centuries of philosophical debate.
- •Emergence and complexity: Biological systems exhibit emergent properties — life, consciousness, social behavior — that seem irreducible to the properties of their constituent molecules.
“The philosophy of biology cannot simply be a branch of the philosophy of physics; it must be built from the ground up, taking seriously the distinctive features of biological systems.”— Ernst Mayr, Toward a New Philosophy of Biology (1988)
These distinctive features mean that the standard philosophical tools — the D-N model of explanation, Nagel’s model of intertheoretic reduction, the regularity account of laws — fit biology poorly. The philosophy of biology has accordingly developed its own conceptual apparatus, drawing on but going beyond the general philosophy of science.
Darwin’s Philosophical Revolution
Charles Darwin’s On the Origin of Species (1859) is arguably the most philosophically significant scientific work ever published. Darwin did not merely propose a new theory in biology; he transformed our understanding of explanation, teleology, and the place of humanity in nature.
Before Darwin, the apparent design of organisms was the strongest argument for the existence of God. William Paley’s Natural Theology (1802) presented the “watchmaker argument”: just as a watch implies a watchmaker, so the intricate design of the eye implies a designer. Darwin provided an alternative explanation: natural selection, a blind, mechanistic process, could produce the appearance of design without any designer.
“There is grandeur in this view of life, with its several powers, having been originally breathed into a few forms or into one; and that, whilst this planet has gone cycling on according to the fixed law of gravity, from so simple a beginning endless forms most beautiful and most wonderful have been, and are being, evolved.”— Charles Darwin, On the Origin of Species (1859), final paragraph
Darwin’s revolution was not just scientific but conceptual. As the philosopher Daniel Dennett argued in Darwin’s Dangerous Idea (1995), natural selection is a “universal acid” that dissolves traditional ways of thinking about purpose, design, and meaning. The questions raised by Darwin’s theory — about teleology, reduction, the nature of species, the units of selection — remain at the center of the philosophy of biology today.
The three chapters in this part examine these questions in depth. Chapter 25 focuses on natural selection itself: its logical structure, the units and levels of selection, and the fraught relationship between Darwinian explanation and teleology. Chapter 26 takes up the species problem, asking what a species is and whether species are natural kinds or historical individuals. Chapter 27 addresses reductionism and emergence, asking whether biology is ultimately reducible to physics and chemistry.
Chapters in Part IX
Natural Selection & Teleology
Darwin’s theory and the elimination (or naturalization?) of teleology. We examine the logical structure of natural selection, the tautology objection, units and levels of selection, adaptationism and its critics, and the relationship between teleological and mechanistic explanation in biology.
The Species Problem
What is a species? We survey the major species concepts — biological, phylogenetic, ecological — and examine the deeper ontological question of whether species are natural kinds, historical individuals, or something else entirely. The debate has profound implications for taxonomy, conservation, and our understanding of biological diversity.
Reductionism vs Emergence
Can biology be reduced to chemistry and physics? We examine Nagel’s classical model of intertheoretic reduction, the challenge of multiple realizability, supervenience without reduction, strong and weak emergence, downward causation, and the new mechanistic philosophy that offers an alternative to both reductionism and anti-reductionism.
Key Thinkers in Part IX
| Thinker | Key Contribution | Chapter |
|---|---|---|
| Charles Darwin | Natural selection as a mechanism for adaptive evolution | 25 |
| Richard Dawkins | Gene-centered view of evolution; the “selfish gene” | 25 |
| Stephen Jay Gould | Critique of adaptationism; spandrels; punctuated equilibria | 25 |
| Ruth Millikan | Teleosemantics; proper functions | 25 |
| Ernst Mayr | Biological Species Concept; autonomy of biology | 26 |
| Michael Ghiselin & David Hull | Species as individuals, not natural kinds | 26 |
| Philip Kitcher | Species pluralism; 1953 and all that | 26, 27 |
| Ernest Nagel | Classical model of intertheoretic reduction via bridge laws | 27 |
| Alex Rosenberg | Defense of reductionism in biology | 27 |
| Hilary Putnam | Multiple realizability objection to type-identity reduction | 27 |
Essential Readings
- •Sober, E. (1993). Philosophy of Biology, Chapters 1–5. (The standard textbook.)
- •Gould, S.J. & Lewontin, R. (1979). “The Spandrels of San Marco and the Panglossian Paradigm,” Proceedings of the Royal Society B 205.
- •Dawkins, R. (1976). The Selfish Gene, Chapters 1–3.
- •Mayr, E. (1982). The Growth of Biological Thought, Chapter 6: “The Species Problem.”
- •Ghiselin, M. (1974). “A Radical Solution to the Species Problem,” Systematic Zoology 23(4).
- •Nagel, E. (1961). The Structure of Science, Chapter 11: “The Reduction of Theories.”
- •Kitcher, P. (1984). “1953 and All That: A Tale of Two Sciences,” Philosophical Review 93(3).
- •Millikan, R.G. (1989). “In Defense of Proper Functions,” Philosophy of Science 56(2).
Guiding Questions for Part IX
- Does natural selection explain biological design, or merely describe it? Is it a causal mechanism or a statistical summary?
- Can teleological language in biology (“the function of the heart is to pump blood”) be given a naturalistic interpretation?
- Is there a single correct species concept, or are different concepts appropriate for different purposes?
- Are species natural kinds (like chemical elements) or historical individuals (like nations)?
- Can Mendelian genetics be reduced to molecular biology? What would such a reduction look like?
- Is emergence a real metaphysical phenomenon, or just a confession of ignorance?
- Does biology have laws in the same sense as physics, or only historically contingent generalizations?