Introduction – a shift in the concept of genes
There is a running joke among natural scientists that “philosophy of science is about as useful to scientists as ornithology is to birds11This quote is frequently attributed to Richard Feynman, although there is no verifiable source or record of Feynman actually saying this exact phrase.” (Kitcher, 1998; p. 32). Why should neuroscientists grapple with philosophy? Can philosophy inform neuroscience in any useful way? To unpack this question, let us look at the more recent scientific history to evaluate how philosophy has previously contributed to biological debates.
To this end, I want to use the example of evolutionary biology and its relation to philosophy of biology. In the mid-20th century, the discovery of the double helix and the elucidation of the genetic code revolutionized biology and raised profound philosophical questions about the nature of genetic information, heredity, and biological causation. These key developments prompted philosophical reflections on reductionism, determinism, and the relationship between genes and phenotypes. Around the same time, the “hardening” of the Modern Synthesis22The Modern Synthesis refers to the synthesis of Charles Darwin’s theory of evolution and Gregor Mendel’s concepts of heredity into a joint mathematical framework (Huxley, 1942). proceeded (Gould, 1983) integrating Mendelian genetics, Darwinian evolutionary theory, and molecular biology. The Modern Synthesis kindled philosophical discussions about the nature of genes, selection, adaptation, and the relationship between genetics and evolution.
A key concept that underwent significant philosophical scrutiny over time was the notion of the gene. Initially, genes were viewed as units of heredity. With the advent of molecular genetics in the mid-20th century, genes were defined as stretches of DNA that encode specific sequences of nucleotides, which in turn specify the sequences of amino acids in proteins. In other words, genes were conceptualized in a narrow sense, as the open reading frame on the DNA from the start of translation to the respective stop codon (Watson, 1970). The definition of a gene was later expanded to include introns; the 5′ and 3′ UTRs (untranslated regions); regulatory elements, such as promoters, transcription enhancers, and silencers; and eventually also noncoding RNAs (i.e., “non-protein-coding RNAs”33Non-protein-coding RNAs are usually are encoded and transcribed by their own genes (Brosius, 2009)).
The shift in understanding what constitutes a gene was paralleled by another conceptual issue that referred to the biological function of a gene. Initially, biologists talked about genes ”for ” a particular trait or function (Keller, 2000). In classical genetics in the early 20th century, the terminology in use entrenched the notion of a gene ”for ” a particular trait and implied a direct, one-to-one relationship between genes and phenotypic traits. This corroborated the assumption that there would be a gene ”for ” eye color or a gene ”for ” height, and so on. As research progressed, it became clear that the relationship between genes and phenotypic traits is often more complex than a simple one-to-one correspondence. Many traits are influenced by multiple genes (polygenic effects), as well as environmental factors and gene-environment interactions. Additionally, genes can have pleiotropic effects, i.e., a single gene can influence multiple traits.