Physicists are serial offenders when it comes to cross-disciplinary meddling. Whether it’s a theoretical cosmologist claiming to solve consciousness or a professor smugly claiming all other sciences are “soft”, physicists are too often quick to pass judgement on other fields. So, I’m a little worried about coming off that way when I criticize a bad habit in biology of referring to the “dark matter of the genome” or other similar phrases.
Dark matter is a mysterious thing, to be sure: it’s an unknown type of matter entirely transparent to light that constitutes about 80% of all mass in the Universe. However, that’s not to say we know nothing about it. The name “dark matter” may be a placeholder for our ignorance, but the concept is not. The problem with the “dark matter of the genome” or what have you is that it uses “dark matter” to mean something we see, but don’t know what it does. That’s almost the conceptual reverse of what it means in physics. After all, the “dark matter” in genes is still part of DNA are still genes: still part of the code geneticists have learned to read, even if the function isn’t clear. Researchers can see it and map it, just like other genes. [Update: corrected for clarity and accuracy – see comment below.]
By contrast, we know dark matter is there because of its influence on galaxies and galaxy clusters. We see its presence in the cosmic microwave background and baryon acoustic oscillations. Though we don’t know its identity, dark matter seems to be a particle, and we can even make concrete statements about possible mass ranges. It’s not the same stuff as ordinary matter, and its very invisibility is part of what makes it complicated.
I’m no geneticist. Genetics is a closed book to me, and I haven’t needed to understand it beyond a cursory level. (High school biology inevitably never got much beyond Mendel and his peas, and a bit about Drosophilia.) That’s OK: I trust my geneticist colleagues, and I get the gist of what they write. If I ever needed to delve into it more deeply, I like to think I’m smart enough to learn. I don’t presume to tell biologists how to study their topic (the very idea is frightening anyway). However, I really would like to see an important concept in physics not be misapplied. From what I can glean, the “dark matter of the genome” is an important subject, one worthy of something better than what amounts to a really bad metaphor.
Galileo's Pendulum 
7 responses to “Please don’t use “dark matter” to mean “something we don’t understand””
I completely agree, just one little thing: what most biologists call “dark matter” of the genome, junk DNA, etc…is actually non-coding DNA (i.e. not genes), so when you say “After all, the “dark matter” in genes are still genes” it sounds contradictory. Anyhow, I know what you mean and agree with you.
That’s a good point. I’ve updated the post to hopefully be a bit clearer – thanks!
I think the reason it is used is the same reason people believe(d) in a ‘dark side of the moon’; dark indicates mysteriousness, being hidden, obscured or unknown. Metaphors for such things are surprisingly thin on the ground. Dark matter has entered the public consciousness as something ‘out there’ that we don’t entirely understand so its name is invoked a lot.
Plus the metaphor isn’t too far-fetched; in the case of the genome we know that the ‘dark matter’ is, if not genes, made of the same DAN as the rest of the molecule (in the same way dark matter is matter, not radiation, negative pressure or something else) and we can even state a few things about its properties (it contains a lot of repetitive sequences, especially AGAGAG…; it contains broken genes, transposons and nonfunctional viruses, we know how often it’s transcribed and how tightly it’s packed, how it varies between people…)
The big ‘? for dark matter appears to be the exact identity of its particle whereas for ‘dark DNA’ it is the function. neither are completely unknown weird stuff nobody understands but rather two complex areas of ongoing research that don’t have all the answers yet.
Hey the Physicists don’t have the patent on Hype. :) :) :)
I hate to do this folks, but when has science ever been able to prove the existance of something that is completely invisible,unmeasurable, yet everywhere???..and based soley on the belief that it must exist because of it’s great influence on galaxies, and exists in cosmic microwave background, in acoustic ocillations (sound) is a particle and a wave…. and is not ordinary matter, invisible and quite complicated….
sounds omnipotent……
can you debunk an invisible man in the sky based on its invisibility, unmeasurable properties and great influences in galaxies or is that quite complicated????
I suspect you’re trolling, but my point is that dark matter is measurable. We have very good evidence for its existence, which I and many others have written about on many occasions. All the links in the post above discuss specific phenomena where we have evidence for dark matter, and the nature of that evidence.
I would posit two examples, the ether (the medium light was supposed to travel through) which has been debunked and the neutrino (small invisible hardly interacting particles.) that have been strongly confirmed.