Genes: from instruments of thought to the base of life
Updated: Sep 13, 2022
Does the way we think about scientific entities matter to scientific practice? Does it make any difference to be realist or anti-realist about scientific entities such as quarks, electrons or nucleic acids? A complete answer to these questions would require a more detailed analysis, but there are some examples from the history of science that show that how we think about the world influences scientific practice.
An interesting case in this regard is the history of the gene. Thinking about the gene in anti-realist or realist terms influenced the way research was conducted. Briefly, being realist about scientific entities means that we take the entities postulated by scientific theories – even those that we cannot observe – to correspond to something real in the world. By contrast, the antirealist is not committed to the existence of the entities, but often just to their utility: they are useful conceptual instruments for making sense of the world and for predicting its behaviour. However, to understand what is the relationship between the history of genetics and the realist/anti-realist approaches, we need to jump a century back in time.
From a concept to a molecule
Between the end of the 19th century and the beginning of the 20th, scientists were discussing the foundational principles of the living world. The theory of evolution provided solid explanations for how biological beings change over time; while genetics started to develop theories to solve the puzzle of the stability of the traits across generations.
After Mendel’s studies on fertilisation and breeding of the pea-plants Pisum sativum, other scientists also started to explore systematically how traits were transmitted. In 1900, three papers on the laws of genetics were published in the Proceedings of the German Botanical Society by three biologists d. Vires, Correns and v. Tschermak. Scientists agreed that something was transmitted in a discrete way from parents to offspring following precise probability distributions. But what? Darwin had already suggested “gemmules”, d. Vires spoke instead of “pangens” and Weismann of “determinants” – all characterised by different properties and having a different nature. Gemmules, for instance, were thought to be shed by various organs and then transmitted via reproduction; pangens were thought to be particles bigger than chemical molecules but smaller than cells that could multiply and grow; determinants were entities that were present in every cell, but only one of them – the relevant one - was active. But to which entities should scientists commit? Which nature was the most explanatory one? The choice was difficult.
Given the challenge of determining which of the proposed entities was the right one, Johannesen in 1909 suggested a solution that was not new in the history of science. He introduced the gene as a new entity “free from any hypothesis” and without theoretical pre-assumptions. Moreover, he didn’t simply suggested this entity; he also proposed the gene as a simple “convenient notational concept” to explain the transmission of traits. No commitment on special properties or on the existence of this entity was needed. No gemmules, nor determinants nor pangens with specific natures. On his view, genes were then not shed by organs nor special microparticles nor active or inactive entities; they were simply a concept to indicate what is transmitted. This is how the gene entered the history of the life sciences: as a useful conceptual instrument.
This was a handy solution. Given that scientist couldn’t observe what is transmitted across generations, they started doing the science of the transmission using only conceptual tools. In the philosophy of science, these tools are called “instrumental theoretical entities”, entities whose observation isn’t needed (or searched), but whose postulation improves the explanations and predictions of a theory. Given the complexity of being realist about the transmitted entities (because it was difficult to understand which properties were more relevant), being simply instrumentalist disentangled the discussion.
Nevertheless, the successes of the gene entity led some scientists to detect more and more of its properties (even if indirectly) and this opened the possibility of a material identification. What if we could be realist about genes? This possibility created a tension between those scholars who preferred to continue to operate within an instrumentalist framework and those who wanted to explore a realist approach. Among others, Herman Muller – a student of Thomas Morgan, one of the fathers of modern genetics – suggested that genes could be chemical molecules that could be discovered and observed. This change of perspective towards a realist approach influenced the research on the gene by motivating the actual search for it. The results started to arrive 30 years later. In 1944, Avery and his team discovered the DNA and this was associated with the location of the gene: genes could be bits of DNA. This then led the construction of a model for DNA structure and replication by Watson and Crick, thanks to x-ray diffraction images of DNA taken by Gosling, Franklin and Wilkins. From this moment, the gene had found a home - the DNA - and scientists started to understand its identity.
From the 1960s onwards genetics was able to offer a realist and material definition of the gene. Genes were defined as segments of DNA located on a chromosome that could be transcribed and then translated into specific amino acids sequences. The famous Crick-sequence hypothesis was formulated as well: each codon - sequence of three bases - specifies only one amino acid and a gene is a sequence of codons that specify for a polypeptide. From being an instrumental entity the gene became a material and identifiable one: contemporary molecular biology and genetics were born.
Changing idea matters
Going back to our original question, that scientists started to think of the gene as something truly existing influenced how the research was done. It was the search for a material basis for the gene that led them to postulate a correspondence between genes, segments of DNA and amino acids. These discoveries were obviously dependent on the possibility – provided by new technological instruments – of actually searching for these entities. Nevertheless, the shift from an instrumentalist understanding to a realist one made (part of) the difference.
The history of the genetics saw the gene concept growing and developing throughout the years even more. But the first 60 years of it show that we shouldn’t be indifferent to how we think about the scientific entities postulated by the various theories and that changing perspective matters.
Concluding, the moral of the story is not that we should always be realist. Rather it is that the different approaches can be fruitful in different moments of scientific analysis. In the beginning, an instrumentalist approach to the genes was efficacious. It was a moment in which the research needed to start in the simplest way possible – and the other entities postulated were complicating the framework and scientific practice. However, once scientists started to learn more about genetic properties, a realist approach allowed the search for a material entity and to new discoveries that changed contemporary science. In other words, how we think about scientific entities has mattered in the past and can still have an impact on how future research can be developed.
Some references and further readings
Bellazzi, Francesca. 2022. “The emergence of the postgenomic gene”. European Journal for Philosophy of Science. 12, 17.
El-Hani, Charbel N. (2007). “Between the cross and the sword: the crisis of the gene concept”. Genetics and Molecular Biology. 30 (2). S. Paulo.
--- 2015. “Mendel in genetics teaching: some contributions from history of science and articles for teachers". Science & Education 24: 173-204.
Fogle, Thomas. 1990. “Are genes units of inheritance?”. Biology and Philosophy 5: 349-371.
Fox Keller, Evelyn. 2000. The Century of the Gene. Cambridge MA: Harvard University Press.
Griffiths, Paul and Karola Stotz. 2013. Genetics and Philosophy. Cambridge UK: Cambridge University Press.
* Francesca Bellazzi is a PhD researcher in the ERC Metascience Project “The Metaphysical Unity of Science” (grant agreement n. 771509) at the University of Bristol. In her research, she investigates biochemical natural kinds and the relations between chemistry and molecular biology.
** You can read Francesca's latest publication "The emergence of the postgenomic gene" here.