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.