This blog post explores whether modern life sciences can be sufficiently explained through the philosophy of science of Karl Popper and Thomas Kuhn, or if a new philosophical perspective is needed.
When naming the two figures who shaped philosophy of science as a contemporary discipline, Karl Popper and Thomas Kuhn undoubtedly come to mind. While they held significantly different views on the nature of science, they share the commonality of being contemporaries who lived through the 20th century and made major contributions to establishing philosophy of science as an academic field. Reading their discussions reveals an intriguing point: despite their starkly divergent views on science, both developed their arguments based on the physical sciences. This becomes clear when examining their academic backgrounds. Popper was born in 1902 and spent his youth during the era when the theory of relativity and quantum mechanics were being established. Thomas Kuhn, while preparing his doctoral thesis in theoretical physics, encountered the history of science and became a philosopher of science. Consequently, it is only natural that both men centered their discussions around physics. In the preface to the fourth edition of Kuhn’s seminal work, The Structure of Scientific Revolutions, philosopher of science Ian Hacking aptly points this out while mentioning Popper.
Hacking also makes another significant observation. Referring to the advent of biotechnology and the 2009 150th anniversary celebration of On the Origin of Species, he states that “since the life sciences have supplanted physics as the leading field in science,” we must ask ourselves whether Kuhn’s theory can be applied to the life sciences. His words may sound somewhat exaggerated, but it is true that biology has developed rapidly since the latter half of the 20th century, greatly increasing its importance within science. Therefore, considering whether existing theories of the philosophy of science can be applied to biology is a meaningful endeavor.
However, this endeavor faces one significant challenge: biology is composed of two fundamentally distinct fields. Recalling Hacking’s point, while biotechnology and evolutionary theory clearly belong to biology, a distinct gap exists between them. To illustrate with a more everyday example, while TV documentaries expose us to the ecology of diverse organisms, the early sections of university biology textbooks are mostly devoted to chemistry and the functions of biomolecules. Both deal with living things, yet their focus is fundamentally different.
Professor Woojae Kim of the University of Ottawa, a fruit fly geneticist, explains this difference in his review of ‘The Fruit Fly: The Hidden Protagonist That Changed the History of Biology and Genetics’ as stemming from two distinct traditions within biology. The tradition of natural history or natural science evolved into evolutionary behavioral biology or evolutionary ecology, while the tradition of physiology merged with physics and chemistry to form molecular biology. Martin Brooks, in *The Fruit Fly*, divides modern biologists into reclusive and field-oriented types. The reclusive type, inheriting the tradition of experimental biologists, conducts research indoors and suffers headaches when exposed to sunlight. They are represented by biochemists, molecular biologists, geneticists, and biologists who develop mathematical models. In contrast, the outdoor types are unfamiliar with laboratories, and ecologists belong to this category.
The dissimilarity between these two fields stems from their different starting points. The problem is that the natures of these two fields differ so greatly that it is difficult to encompass both with a single scientific philosophical explanation. For example, evolutionary biology can be better explained by Kuhn’s philosophy of science than by Popper’s. Because the timescale of evolution exceeds human lifespans, verifying evolution through experiments is difficult. Furthermore, although evolutionary theory has undergone numerous revisions since its initial proposal, it remains firmly established as the theory explaining many phenomena in the biological world, with no competing paradigm currently existing. Evolutionary theory takes the form of Kuhn’s normal science; while it is not a dramatic scientific revolution, it cannot be said that there was no paradigm shift. Since Darwin, various theories about the mechanisms of evolution have been proposed, and the Modern Synthesis is now established as the standard theory of evolution. While this does not perfectly align with Kuhn’s theory of scientific revolutions, it can be seen as a similar case to how Newtonian mechanics still holds recognized value.
Conversely, molecular biology is a field where falsification, as Popper described it, actively occurs. For example, the Central Dogma of molecular biology proposed by Crick was falsified by viruses with RNA genomes. In molecular biology, research is conducted using physical and chemical methods within laboratories, making verification and falsification relatively easier than in evolutionary biology. However, molecular biology lacks a single paradigm like Newtonian mechanics or relativity theory. Since the Central Dogma was disproved, no new paradigm encompassing it has yet emerged.
How should we approach phenomena that are difficult to address from a unified perspective across these two fields? It is important to remember that these two disciplines are complementary rather than antagonistic. This is well illustrated by the concepts of ultimate causation and proximate causation. For example, when considering why moths fly toward light, the answer that it was advantageous for survival is an ultimate explanation, while the answer that the moth flies toward light due to neural impulses transmitted from light receptors is a proximate explanation. These two concepts are not opposites but complementary; evolutionary biological explanations can be considered ultimate explanations, while molecular biological explanations are proximate explanations.
Viewed this way, existing theories in the philosophy of science alone struggle to explain the essence of biology. While the way theories are developed in physics has not changed significantly, biology consists of two distinct fields. Therefore, different perspectives must be applied according to the characteristics of each field, or a new perspective capable of encompassing both fields is needed. For example, new perspectives could be derived from the results of statistical physics or complex systems physics. The crucial point is that simply applying existing philosophy of science is insufficient.
I will conclude this essay with the thoughts of the philosopher of science, Feyerabend. He argued that great scientists were not bound by specific methodologies, and that science can only be truly scientific when diverse hypotheses are presented without constraints. This is remarkably similar to the conclusion discussed in this essay regarding the philosophy of biology. Diverse discussions on the philosophy of biology must be presented. Attempts to define biology solely through existing discussions would be an act that stifles imagination and creativity, regressing human intellect.
