This blog post critically examines whether Kuhn’s paradigm theory can be validly applied to biology through examples from genetics and evolutionary theory.
In everyday life, the term ‘paradigm’ is a very commonly used word. When the way we explain a situation undergoes a major shift, people generally say the paradigm has changed. The starting point for the term ‘paradigm’ becoming commonplace among the general public is Thomas S. Kuhn’s book, The Structure of Scientific Revolutions. The Structure of Scientific Revolutions presented a new perspective on the methodology of science to philosophers of science. The ‘paradigm’ Kuhn proposed in this book refers to the scientific theories or frameworks formally accepted by the entire scientific community during a specific period in the history of science. Indeed, the paradigm and scientific revolution theory effectively explain historical scientific cases, such as the revolutionary shift from Newtonian mechanics to Einstein’s theory of relativity or Kepler’s years-long struggle regarding the motion of Mars. However, it is important to note that the examples supporting the book’s content are largely confined to physics. This could be explained by the fact that Thomas Kuhn majored in physics at Harvard University. However, to call Kuhn’s theory of normal science a philosophy of science theory, it is necessary to analyze whether Kuhn’s theory of normal science can indeed be applied to other fields of science. Therefore, let us consider whether Kuhn’s philosophy of science theory can be applied to biology, which is recognized as forming one pillar of modern science, and thereby examine the validity of Kuhn’s philosophy of science theory.
Since research on paradigms in biology remains limited, debates may arise over which theories constitute biological paradigms. Therefore, we will first clearly define what Kuhn means by a paradigm before proceeding with the discussion. In The Structure of Scientific Revolutions, Kuhn states that a paradigm is an achievement satisfying two characteristics: First, the achievement must be sufficiently unprecedented to detach a group of tenacious advocates from the competitive mode of scientific activity. Second, the achievement must be sufficiently flexible to leave all types of problems open to solution by the reorganized group of researchers. Let us call a theory that satisfies these two conditions a ‘paradigm’.
The two most significant fields in the history of modern biology are ‘evolutionary theory’ and ‘genetics’ as studied in molecular biology. To answer the two questions about the origin of life and the continuity of life, biologists conducted diverse research and progressively refined their theories. In genetics, the ‘gene particle theory’ has prevailed in its struggle against the ‘gene blending theory’ and is now accepted as the established theory by many molecular biologists. This has made significant contributions to major molecular biological discoveries in the history of biology, such as Mendel’s laws of inheritance and Watson and Crick’s discovery of the double helix structure of DNA. Darwin’s theory of evolution, too, may have faced criticism from many scientists in the past. However, compared to other theories, evolutionary theory currently provides the best explanation for life’s adaptation and change. Scientists use evolutionary theory to solve major problems in biology, such as the origin of new species and population genetics. Therefore, both theories satisfy Kuhn’s definition of a paradigm.
According to Kuhn’s theory, the history of science is explained through the stages of pre-normal science, paradigm formation, the normal science process, crisis situations, and scientific revolution. Let us analyze whether the history of genetics research follows Kuhn’s theory of normal science. Among the numerous theories attempting to explain how traits are inherited by offspring, the two most influential were the ‘blending theory’ and the ‘particle theory’.
The theory of blending posited that parental genetic traits blend to appear in offspring, much like mixing blue and yellow paints produces green. In contrast, the theory of particles argued that heredity occurs because parents transmit some particulate unit capable of inheritance to their offspring. The blending theory was discarded because it inevitably concluded that offspring would possess increasingly similar traits over generations. The particle theory gained paradigm status after it was revealed to explain genetic laws such as the law of dominance, the law of independent assortment, and the law of segregation. Following the establishment of this paradigm, normal scientific research focused on identifying what these genetic particles actually were. Biologists discovered that the genetic particles were not proteins but DNA, and subsequently dedicated themselves to uncovering DNA’s coding mechanism and structure. Furthermore, based on the particle theory, research into the behavior of chromosomes progressed, enabling biologists to understand the underlying causes of genetic laws. Observing the history of genetics research reveals that studies continue to this day centered around the paradigm of the ‘germ cell theory’. In other words, we can find Kuhn’s theory of the philosophy of science within the history of genetics.
However, consider the case of evolutionary theory. Darwin’s theory of evolution was proposed when he published ‘On the Origin of Species’ in 1859. Yet, evolutionary theory did not emerge as a solution to a specific problem at a particular moment. It arose through the accumulation of diverse facts. First, the fact that archaeologists determined the Earth’s age to be older than that indicated in the Bible, the fact that Paley’s populations overproduce, and the fact that Malthus’s limited resources lead to survival competition among individuals—these combined to give rise to it. Moreover, it took nearly 80 years after Darwin’s 1859 publication for evolutionary theory to become established as a ‘paradigm’. Until genetics explained the possibility of variation in the early 1900s, Darwin’s theory was not widely accepted. The observation of diverse phenomena provided the foundation for accepting evolutionary theory. This demonstrates that evolutionary theory did not undergo the ‘Gestalt shift’ described in Kuhn’s philosophy of science. The foundation for accepting evolutionary theory accumulated over time, and consequently, the theory that could explain this foundation inevitably gained acceptance. It is questionable whether the normal scientific process continues even after evolutionary theory was recently established as a paradigm. While scientists explain various phenomena based on evolutionary theory, biologists like Gould still exist who, while claiming to be Darwinists, advocate for punctuated equilibrium—a theory that contradicts gradualism, one of the pillars of Darwin’s evolutionary theory. This does not correspond to what Kuhn describes as ‘theoretic clarification’ or ‘crisis’. Theoretical clarification is a phenomenon occurring within normal science, enabling a theory to clearly explain aspects it previously struggled with. However, punctuated equilibrium is fundamentally contradictory to a core part of Darwin’s theory, making it difficult to view this as clarification. Furthermore, a crisis of paradigm arises from anomalous cases, progressing either by rejecting the theory or by forcing the anomalous cases to fit the theory. However, the case of punctuated equilibrium does not fit either of these directions. It represents a process that cannot be explained by Kuhn’s theory of the philosophy of science.
The question of why research on heredity appears to follow Kuhn’s paradigm theory well, while evolutionary theory does not, as seen in the historical examination of heredity and evolution presented earlier, can be explained by introducing the concept of ‘emergence’. It is generally said that living organisms possess ‘emergence’. Emergence refers to a property where the whole cannot be explained solely by the individual characteristics of its microscopic parts; it can be expressed as ‘the whole is greater than the sum of its parts’. One field of study that inevitably must address emergence is ‘neuroscience’. Neuroscience, which studies the brain and the consciousness it produces, does not explain consciousness as simply arising from the sum of neurons or nerve cells. Some emergent characteristic, not yet understood by scientists, creates human consciousness through the sum of neurons. Neuroscience has not yet formed a ‘paradigm’ as Kuhn describes. Neuroscientists are interested in explaining individual neural phenomena and rarely attempt to discover any overarching law encompassing all of them; even if they do attempt it, discovering such a law through experimentation is not easy. Rather, this is studied as the domain of philosophers or psychologists. The reason is that disciplines possessing emergent properties find it difficult to establish paradigms. Disciplines with emergent properties give rise to complex characteristics that cannot be reduced to just a few theories. To form a paradigm, a theory capable of solving diverse problems must emerge; however, if emergent properties exist, solving problems with a single theory becomes impossible, making the birth of a paradigm difficult. The absence of paradigms in most fields of biology can be attributed to this very emergent nature of biology. Consequently, since discussing paradigms themselves is largely impossible in most biological fields, analyzing the history of biology through Kuhn’s philosophy of science theory holds little significance.
Genetics can be viewed as a branch of molecular biology. Molecular biology is a discipline that introduced a representative form of reductionism, explaining the laws of inheritance through the behavior of genes and chromosomes. In contrast, research on evolutionary theory exhibits emergent characteristics that cannot be explained by a single law. Darwin’s theory of evolution alone consists of at least five distinct components: the steady evolution of organisms, the theory of common descent, the theory of speciation (diversification of species), the theory of gradualism, and the theory of natural selection. This supports the earlier explanation that Kuhn’s philosophy of science theory fails to adequately describe disciplines exhibiting emergent properties.
Thus far, we have examined how the application of Kuhn’s philosophy of science theory differs between genetics and evolution—the two fields constituting biology—and what causes this difference. Kuhn’s theory applied well to genetics but failed to provide an adequate explanation regarding evolutionary theory. We have also seen that this difference stems from distinctions related to the ‘emergence’ inherent in these two branches of biology. To summarize the discussion, Kuhn’s theory of the philosophy of science has limitations in explaining disciplines characterized by emergence, and consequently, it does not adequately account for the emergent nature of biology. Applying Kuhn’s theory to biology requires consideration of whether the gradual changes in theory or the variously intertwined theories occurring in biology can be simply explained by paradigms. Furthermore, it becomes apparent that a new theory of the philosophy of science is needed to explain the history of biology. While Kuhn’s theory is not entirely invalid in biology, it is indeed questionable whether applying it makes sense in biology, where paradigms are almost non-existent due to emergence. It seems necessary for the philosophy of science community and biologists to collaborate to derive a theory that can adequately explain the history of biology.
