Genes are our modern idiom for itemizing life’s variety and explaining human nature. We say there are genes for intelligence and shyness, genes for aggressiveness and maternal love. Researchers get billions from government agencies to carry out “genome-wide association studies” that promise to wrestle down and eventually vanquish disease. Like the atom in physics, the gene is a building block that helps us describe reality.
But are genes, as a concept, here to stay?
Wilhelm Ludvig Johannsen, a Danish botanist with round spectacles and a little white goatee, coined the term in 1909. To his generation, the “gene” was a heuristic that helped make sense of breeding experiments in fruit flies. Its Greek etymology (from genea, as in generation) divulged its significance: Genes were things out of which other things arise. It made sense to mentally situate them on the chromosomes, but no one knew what a gene was made of or had seen one.
All that changed when James Watson and Francis Crick came along. With their discovery of the double helix structure of DNA in 1953, a definition soon presented itself: A gene was a stretch of DNA which, copying itself with surprising fidelity, encoded a working protein. “One gene, one enzyme,” became the creed.
Except that this was a massive simplification. Nine out of 10 human genes, scientists soon learned, have at least one alternative form of expression — meaning that two people could have the exact same gene, but an entirely different manifestation of it. And there was another level of complexity: One person’s gene might express itself differently if that person is in a cold versus a warm environment, at base camp or at peak altitude, in the morning or at night. (In the fruit fly there is a gene that can produce 36,016 distinct biochemical substances, called products, depending on circumstances.) Making a single protein often entails using pieces of many different genes strewn all over the genome. Some people now wonder whether it makes sense to speak of independent genes at all.
But there is something even more damning. For more than a century, schoolkids have been taught that Austrian monk Gregor Mendel discovered dominant or recessive genetic traits by breeding peas to see what made them straight or wrinkled, green or yellow. But as the science educator Kostas Kampourakis argues in his book “Making Sense of Genes,” there is no “gene” for wrinkled peas, only one that plays a role in the formation of an enzyme that synthesizes starch — and when there’s enough of that enzyme there is more osmosis, leading to a wrinkled pea. There is no “gene” for the color green, either, but rather genes that affect the metabolism of chlorophyll. The biology is just too complex to say that a certain gene leads to a particular characteristic.
Likewise, it is not DNA that directly determines disease, but faulty proteins. Defective hemoglobin gives you ß-thalassemia, and low-density lipoprotein produces familiar hypercholesterolemia. Genes do not dictate who we are, but instead provide a primary resource for unique cells to draw upon as they develop in different environments. They can do nothing on their own, writes the philosopher of science Evelyn Fox Keller, so why do we speak of genes doing anything at all?
We do so for the same reason we describe electrons “jumping,” galaxies “exploding,” birds and monkeys “falling in love.” Because science is a form of competitive storytelling. It gives names to things and produces narratives based on a method that has undergone impressive refinement. But even stories that rid us of disease or take us to the moon are still stories. There can be no science without the use of metaphor.
Genes are central to our human narrative at this moment. They’ve been spliced between plants to resist pests and improve our crops. They’ve been edited to one day allow for safe transplants of organs between pigs and humans. They help us discover our ancestry, and our propensity for disease. It might be hard right now to imagine a world without genes. But 15th century astronomers couldn’t imagine the heavens without epicycles and 19th century physicists couldn’t imagine the propagation of light without an ether.
We’ve come a long way using the story of genes. But is this really the best way to describe the biology of life?
What we have learned over the past 30 years is that there is never just one gene trigger for a trait, but rather a complex interaction of material from disparate parts of the genome. In light of this, we might consider adopting the metaphor of violin strings, which produce unique sounds as a result of thickness, but also the violinist’s fingering and bowing. The gene as a discrete entity may, in some sense, not exist at all.
So what should we do? One idea is to drop the gene-speak altogether and talk about DNA instead. Another is to apply the term “gene” to the actual molecules whose code is translated into proteins, called messenger RNAs. Yet a third is to shift the whole narrative to proteins, because that’s what we need to fix when things go wrong.
None of these changes are imminent. Today we seem to need genes to describe our diseases, emotional states and proclivities, to decide whether to chop off our breasts prophylactically, or even to beg for lighter sentences in the courtroom. But will “genes” still be around 100 or 200 years from now? Ask the epicycles and the ether.