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Applying the traditional approach of scientific metaphysics to the best biological theories of 1930s

Morgan was a meticulous empiricist, and he tried to avoid letting speculation enter into his scientific writings. But scientific metaphysics is by its nature speculative, and it is fair to ask how hypothetical scientific metaphysicians in the 1930s might have answered the question, “What is a gene?” Could their answer to this question provide a basis for answering questions about the fundamentals of heredity, development, and evolution?

Bold scientific metaphysicians of the 1930s (and it is fair to assume that these hypothetical metaphysicians would have been as bold as today’s real ones) might have claimed that since presumably every stable inheritance pattern can be attributed to gene differences, that genes must be thefundamental constituents of heredity. In fact, many biologists, until quite recently, have written in textbook expositions and glossaries that genes are the “fundamental units of inheritance.” What does it mean to say the gene is the fundamental unit of heredity? Presumably it means that if you could identify every gene and every difference in every gene, and if you could trace the transmission of each gene and each gene difference from one generation to the next, then you would have a comprehensive basis for understanding everything about heredity.

Scientific metaphysicians of the 1930s could have gone further. Since differences in genes cause phenotypic differences by affecting the way organisms develop, genes might also be thefundamental units of development. What would this mean? It would mean that if you could identify every gene and the functional role of every gene, then you would have a comprehensive basis for understanding everything in development. A scientific metaphysician of the 1930s would not need to speculate about the role of genes, but they could draw on the success of the transmission theory to claim that genes must have functional roles of some kind, and that fulfilling these roles must provide the fundamental basis underlying the development of organisms.

Although this might appear excessively speculative, consider the point that many contemporary metaphysicians take to be a marker of metaphysical significance: unification (e.g., Ladyman et al. 2007; Ladyman this volume, chap. 7). Identifying the gene as the fundamental unit of both heredity and development would unify their understanding of these phenomena. With the establishment of classical genetics, the science of heredity (genetics) and the science of development (embryology) had become disunified. But by going to the fundamentals, a metaphysician could have exclaimed, “This metaphysical interpretation reveals an underlying unity of nature!” This would be viewed as a basis for confidence. But why stop with the processes of inheritance and development?

Scientific metaphysicians of the 1930s might have wondered whether genes could also be the fundamental units of evolutionary change. Evolution involves the inheritance of changes in the forms of organisms over many, many generations. This must involve the inheritance of changes in the way organisms develop these forms. So, the metaphysical interpretation might go, genes must be the fundamental units of evolutionary change. Again, we could ask, what would this mean? Presumably, it would mean that if you could identify every gene and every difference in every gene that has occurred in evolutionary history, if you could identify the first appearance of each of these genes and gene differences, and if you could trace and explain the changes in frequencies of these genes and gene differences, then you would have a comprehensive basis for understanding evolution.

Scientific metaphysicians in the 1930s could have appealed to the latest developments in evolutionary theorizing and drawn upon the abstract theoretical work of Fisher, Haldane, and Wright to substantiate this view. The unification of fundamental principles of evolution with the fundamental unit of heredity and development could have made this interpretation of the best scientific theories of their day extremely appealing.

Of course, I am not advocating the idea that genes really are the fundamental units of heredity, development, or evolution, or even the more modest idea that scientists and philosophers of the 1930s had good reason for believing this. After all, section 3 shows that analyzing the classical concept of the gene in the context of scientific practice (rather than abstractly) reveals that there was good reason not to view classical genes as fundamental units of inheritance. The aim of this section is to show that today’s favored approach to scientific metaphysics is unreliable. We can see this because if philosophers of the 1930s used this approach to identify the fundamentals of life, and if they analyzed the transmission theory and explanations in an abstract fashion (i.e., not in terms of the role they played in the context of investigative practice), they could have erroneously concluded that genes are the fundamental units of heredity, development, and evolution.

 
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