What is ‘junk DNA’?

I’m always hearing people bring up the modern understanding of ‘junk DNA’ as if it somehow lends evidence to the existence of God. It’s not an argument I really get. Whether most of an organism’s DNA is needed or not doesn’t magically disprove evolution. Maybe people just don’t get the concept, I don’t know. I’ll try and give a brief explanation.

About 30 or 40 years ago it was understood that most of the human genome was composed of DNA that served no discernible purpose. That understanding changed with time, morphing from a position of no purpose to one where most DNA was noncoding. This was partially a technical change. Most DNA is noncoding; it doesn’t produce proteins. “Junk” is a misnomer in this context. But we’re discovering more and more that previously deemed purposeless DNA actually does have a function. Often enough it is important in regulation. But still, some 95% of our DNA has no function at all. We may be finding that more of it serves some purpose than we previously thought, but the fact that most of it is useless remains.

I bring this up because of a recent post I saw on an anti-science website (better known as the inspiration for my still-new Punching Bags series – I use it as a hunting ground now). What I find so entertaining about these creationists and their infatuation with junk DNA is that one of the reasons biologists (not creationists, of course) are able to determine that DNA has a function is because of evolution. Sometimes we can directly determine a function through experiment and observation, but much of the time we rely upon inference. DNA which is noncoding yet none-the-less conserved is said to have some sort of function. It must. It makes no sense for a given sequence to exist over millions of years and across distant lineages if it doesn’t serve some function. Of course, this is no problem for those of us on the side of science. Everything really does make sense in the light of evolution. (And you thought that saying was just rhetoric.) But this does pose a problem for creationists. While they’re trying to inanely deny that most of our DNA is not usefully transcribed, they are necessarily relying upon the fact of evolution – the very thing they want to deny.

If it wasn’t for the harm to all of science they cause, I would more easily delight in pointing out how ill-considered creationist ideas really are.

10 Responses

  1. I’m not disagreeing with you, but “it must.” isn’t much of an argument. It mustn’t do anything. I’m sure there are useless bits in our DNA, it’s probably more efficient to “preempt” old stuff instead of paring out all of the useless things.

    Vestigial is probably a better word if indeed there are unused chunks.

  2. Conserved DNA must have some function because otherwise it would mutate and degrade over time.

  3. Perhaps. But given our lack of comparable DNA from very far back…

  4. Conserved DNA can be thought of in terms of being compared DNA. The same noncoding genes in one species will be the same as in another species, even though they may be separated by millions of years.

  5. It’s not an argument I really get.

    The argument is very simple:
    1: “junk” DNA actually has some function, so is not junk.
    2: therefore evolutionists were wrong.
    3: therefore evolution is refuted.
    4: therefore creationism is true.

    It is an utterly stupid argument, but that seems to be the way that many creationists and ID proponents think.

  6. I’m glad you posted this. For a post I just stuck up today about science denial, I had drafted all this material about ‘junk DNA’ and its relationship to creationism. In the end I decided the topic was too heavy to just toss in as a quick example.

  7. One of the things I find personally find frustrating in these online evo-creo debates, is that I’m not particularly knowledgeable about biology or evolution. I wish more people who have actually studied biology, like yourself, would get involved in blogging and commenting on other blogs like Eternity Matters. I’ve weighed in on evolution topics there before, but I can only link to what others have said and talk around the principles in general. Having said that, a more knowledgeable person could come in and comprehensively annihilate their points – and the same argument would appear again a couple of months later as though nothing had happened.

  8. I have commented on Neil’s anti-science site. Unfortunately, he decided to moderate my comments because I refused to engage in a red herring, instead choosing to challenge him to defend what he believes (he couldn’t). As a result, I don’t seem him as particularly trustworthy.

  9. […] post was primarily about so-called ‘junk DNA’, but I’ve addressed that topic in the past, so I will only mention it to note that it only ever betrays a deep ignorance when creationists […]

  10. […] post was primarily about so-called ‘junk DNA’, but I’ve addressed that topic in the past, so I will only mention it to note that it only ever betrays a deep ignorance when creationists […]

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