philosophy of biology

Teleology from Aristotle to Kant

The philosophy of biology, like all of Western philosophy, began with the ancient Greeks. Although Plato (c. 428–c. 348 bc) was little interested in the subject, his student Aristotle (384–322), who for a time was a practicing biologist, had much to say about it. From a historical perspective, his most important contributions were his observations that biological organisms can be arranged in a hierarchy based on their structural complexity—an idea that later became the basis of the Great Chain of Being—and that organisms of different species nevertheless display certain systematic similarities, now understood to be indicative of a common evolutionary ancestry (see homology). More significant philosophically was Aristotle’s view of causation, and particularly his identification of the notion of final causality, or causality with reference to some purpose, function, or goal (see teleology). Although it is not clear whether Aristotle thought of final causality as pertaining only to the domain of the living, it is certainly true that he considered it essential for understanding or explaining the nature of biological organisms. One cannot fully understand why the human eye or heart has the structure it does without taking into account the function the organ performs.

The notion of final causality was taken for granted by most philosophers from the Hellenistic age through the end of the Middle Ages. Indeed, philosophers and theologians in the medieval and early modern periods adopted it as the basis of an argument for the existence of God—the teleological argument, also known as the argument from design, which was developed in sophisticated ways in the 19th and 20th centuries (see intelligent design). During the scientific revolution of the 17th century, however, final causes came to be regarded as unnecessary and useless in scientific explanation; the new mechanistic philosophy had no need for them. The English philosopher and scientist Francis Bacon (1561–1626) likened them to the Vestal Virgins—decorative but sterile.

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Despite these criticisms, the notion of final causality persisted in biology, leading many philosophers to think that, in this respect at least, the biological sciences would never be the same as the physical sciences. Some, like the German Enlightenment philosopher Immanuel Kant (1724–1804), regarded biology’s reliance on final causality as an indication of its inherent inferiority to sciences like physics. Others, like the British historian and philosopher of science William Whewell (1794–1864), took it as demonstrating simply that different sciences are different and thus that a form of explanation that is appropriate in one field might not be appropriate in another.

Vitalism and positivism

In the late 19th century, the question of the supposed inherent differences between the biological and the physical sciences took on new importance. Reaching back to the ideas of Aristotle, but also relying on more-recent theories promoted by the Count de Buffon (1707–88) and others, several philosophers and biologists began to argue that living organisms are distinguished from inert matter by their possession of a “life force” that animates them and propels their evolution into higher forms. The notion of an entelechy—a term used by Aristotle and adopted by the German biologist Hans Driesch (1867–1941)—or élan vital—introduced by the French philosopher Henri Bergson (1859–1941)—was widely accepted and became popular even outside academic circles. Ultimately, however, it fell out of favour, because it proved to have little direct scientific application. The difficulty was not that life force was not observable in the world (at least indirectly) but that it did not lead to new predictions or facilitate unified explanations of phenomena formerly thought to be unrelated, as all truly important scientific concepts do.

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The decline of vitalism, as the resort to such forces came to be known, had two important results. Some philosophers tried to find a way of preserving the autonomy of the biological sciences without resort to special forces or entities. Such theories, referred to as “holism” or “organicism,” attracted the attention of the British philosophers Alfred North Whitehead (1861–1947) and Samuel Alexander (1859–1938), who thought that the very order or structure of organisms distinguished them from nonliving things. Others turned to early 20th-century advances in logic and mathematics in an attempt to transform biology into something parallel to, if not actually a part of, the physical sciences. The most enthusiastic proponent of this approach, the British biologist and logician Joseph Woodger (1894–1981), attempted to formalize the principles of biology—to derive them by deduction from a limited number of basic axioms and primitive terms—using the logical apparatus of the Principia Mathematica (1910–13) by Whitehead and Bertrand Russell (1872–1970).

In the first half of the 20th century Anglo-American philosophy (analytic philosophy) was dominated by a school of scientific empiricism known as logical positivism. Its leading figures—Rudolf Carnap (1891–1970), Carl Hempel (1905–97), Ernest Nagel (1901–85), R.B. Braithwaite (1900–90), and Karl Popper (1902–94)—argued that genuine scientific theories, such as Newtonian astronomy, are hypothetico-deductive, with theoretical entities occupying the initial hypotheses and natural laws the ultimate deductions or theorems. For the most part these philosophers were not particularly interested in the biological sciences. Their general assumption was that, insofar as biology is like physics, it is good science, and insofar as it is not like physics, it ought to be. The best one can say of modern biology, in their view, is that it is immature; the worst one can say is that it is simply second-rate.

Twentieth-century resurgence

This uncharitable perspective was soon undermined, however, by at least three important developments. First, in the 1960s the biological sciences became philosophically much more complex and interesting, as the stunning breakthroughs in molecular biology of the previous decade—particularly the discovery in 1953 of the nature of the DNA molecule—were starting to bear fruit. For example, one could now study variation between or within populations quantitatively, rather than simply by estimation or guesswork. At the same time, there were major new developments and discoveries in the theory of evolution, especially as it applied to the study of social behaviour. It was therefore no longer possible for philosophers to dismiss biology as an inferior science merely because it did not resemble physics.

Second, the conception of science advocated by logical positivists came under attack. Drawing on the work of the philosopher and historian of science Thomas Kuhn (1922–96), critics argued that the picture of scientific theories as structurally uniform and logically self-contained was ahistorical and unrealistic. Accordingly, as philosophers broadened their appreciation of scientific-theory construction in the real world, they became increasingly interested in biology as an example of a science that did not fit the old logical-positivist paradigm.

Third, in the early 1960s the history of science began to emerge as a distinct academic discipline. Its rapid growth attracted the attention of philosophers of science and helped to strengthen the new consensus among them that an appreciation of the history of science is necessary for a proper philosophical understanding of the nature of science and scientific theorizing. Significant new work by historians of science on the development of evolutionary theory was taken up by philosophers for use in the explication of the nature of science as it exists through time.

In this newly receptive intellectual climate, research in the philosophy of biology proceeded rapidly, and the influence and prestige of the discipline grew apace. New professional organizations and journals were established, and the area soon became one of the most vital and thriving disciplines within philosophy. Although the philosophy of biology is still marked by a concentration on evolutionary theory as opposed to other subjects in the life sciences, this may simply reflect the fact that evolution is an especially interesting and fertile topic for philosophical analysis.