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In January 2012, David Icke published a book (ISBN: 9780955997334) entitled “Remember where you are and where you come from” in which he challenged what he claimed to be the view of mainstream science that 90–97% of the human genome was “junk DNA”, serving no function. He implied, instead, that it must have a function, but that this was unknown.

Is it still true that we do not know what all this DNA does? I see that we consider this DNA to be non-coding, but does that mean it is “junk”? I find it hard to believe that it can serve no function, otherwise why would the DNA be there? Is it possible that it is used for things we don't yet understand?

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  • $\begingroup$ This question contains more info on what non-coding DNA is, but I think Remi has answered whether or not Icke's claim is right. $\endgroup$
    – JCThomas
    Commented Aug 27, 2017 at 16:08
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    $\begingroup$ @David that's reasonable, but i voted to leave this open and downvoted. I think the reference to Icke's book as the thing that sparked the question, and the actual question (what is junk DNA and do we know what it does) is on topic (general questions about biological concepts). The question could be improved by removing the reference to the book by a professional conspiracy theorist, since it distracts from the actual question about biology. $\endgroup$
    – De Novo
    Commented Feb 25, 2019 at 18:20
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    $\begingroup$ "Junk DNA" is no longer used. This term originated a long time back when the function of the non-genic/intergenic DNA was not known. I'm not sure which "mainstream science" is he talking about! $\endgroup$
    – WYSIWYG
    Commented Feb 26, 2019 at 8:37
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    $\begingroup$ I'm going to urge people not to respond to this unless they are actually working in the field. I don't know of any field in science to which the Dunning-Kruger effect applies more. If you are confident you understand this field, you almost certainly do not. There is a large and highly focused literature on this, and almost no one outside the field even knows the field exists, let alone has read any of the papers in it. If you have not read at least 100 papers specifically on the topic, your answer will be wrong and misleading. $\endgroup$
    – iayork
    Commented Feb 26, 2019 at 16:00
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    $\begingroup$ @David I think your edit to the title implies that it was once thought that "junk DNA" is functionless; it's possible that's the case, but not to my knowledge. Unless you have a reference that in fact junk DNA was thought to be functionless at some point, I think the previous edited title "Does "junk DNA" serve no function?" is much better. $\endgroup$
    – Bryan Krause ♦
    Commented Feb 26, 2019 at 16:14

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What is junk DNA?

The term junk DNA is not used that often in the scientific literature and when it is it is often used very generally, often early in the introduction. It generally refers to any non-coding DNA.

In humans, about 25% of the non-coding DNA is introns and regulatory sequences. These sequences are highly essential for the working of the organism. There are many cases of adaptation from these regulatory sequences (see this answer).

The term junk DNA is very loaded and may make it feel to people that this DNA is not important for the organism survival but this is not quite what was first meant by the term junk DNA. It is true though that repeated DNA such as those in transposable elements are thought to have little impact on the organism phenotype. Transposable elements can however have important role on the evolution of a lineage.

IMO, the claim is false and insulting

By saying things like They do this because they gave no idea what it does and, from their version of reality, it appears to serve no function., it feels to me that David Icke is using the loaded side of the term junk DNA to insult all geneticist in general.

D. Icke is 1) doing a strawman by suggesting that geneticists think that regulatory sequences are of no use and 2) he is suggesting that geneticists are biased and will invent whatever theory in order to match with a pre-conceived opinion of the reality.

About David Icke

I don't mean to make an intentional fallacy but I would like to note that David Icke is a famous conspiracy theorist who has been illogical and obviously opinion based many times. For example David Icke claims that the moon is actually a spaceship and not a natural satellite (see here). He has made many other fantastic claims of the kind. Scroll down the wikipedia article to enjoy some non-sense!

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    $\begingroup$ I know a lot about Icke's material. Some is spot on and some is sketchy, but I don't think ad hominem ever discredits an argument so it's probably best to removed the last paragraph. $\endgroup$
    – Charlie
    Commented Aug 27, 2017 at 15:11
  • $\begingroup$ You say it's 5-10% that's regulatory in the other answer, which I think is more accurate $\endgroup$
    – JCThomas
    Commented Aug 27, 2017 at 16:23
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    $\begingroup$ Remi.b’s last paragraph is neither an ad hominem towards Icke nor should be deleted. Icke’s scientific illiteracy is relevant to conclude that he’s in no position to criticize scientific consensus (but in this case, the consensus of "junk DNA" has been invented). Many of his claims are extraordinary and the evidence provided leaves much to be desired, so what he says has to be taken with a grain of salt. For example, he believes in “monoatomic gold”, a very problematic concept on its own (rationalwiki.org/wiki/ORMUS). $\endgroup$
    – user38945
    Commented Dec 2, 2018 at 18:47
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The term "junk DNA" is not commonly used any more by scientists. It became popular when people realized, that only 1-2% of the human genome encode proteins, and wondered about why there is so much more DNA if it's not needed. But we know today, that it does in fact serve many functions and therefore is now referred to as "non-coding DNA".

Some non-coding DNA functions:

  • regulatory elements: promoters, enhancers or silencers are DNA regions, where transcription or other binding factors bind to DNA to regulate the accessibility of genes to the transcription machinery and therefore control which genes are expressed
  • introns: DNA regions that are inserted into the actual coding region and removed during splicing. They serve a role in RNA processing and alternative splicing.
  • functional RNA: Not being translated into a protein doesn't mean that the RNA produced by a locus doesn't serve a function in the cell (e.g. ribosomal RNAs, microRNAs)
  • structural elements: telomeres and centromeres are important for chromosome stability, sister chromatid linkage, heterochromatin formation and anchoring to the nuclear envelope

We keep learning more and more about different functions of DNA regions. Even open reading frames (ORFs), which encode for functional RNAs or even small proteins keep being identified. It's therefore not true that it does not serve any function, because we have identified many functions. And while we still don't know everything about it, our knowledge is increasing.

Further reading:

Shanmugam et al. 2017 - Non-coding DNA – a brief review

NIH Genetic Home Reference - What is non-coding DNA?

Wikipedia - Non-coding DNA

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  • $\begingroup$ How much of the 90-97% do you think the points you mention cover? The only point that is really new this century is "functional RNA". It may be true that "we keep learning more", but that hardly answers the question. $\endgroup$
    – David
    Commented Feb 26, 2019 at 17:43
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    $\begingroup$ On the other hand large segments of non-coding DNA have been removed from mice with no apparent affect on their phenotype. It's a complex topic that is far from settled. $\endgroup$
    – Charles E. Grant
    Commented Feb 26, 2019 at 18:03
  • $\begingroup$ @David: The question was if if non-coding DNA is junk and has no function as put forward by the quote from David Icke that you edited out of the question, which also implied that scientists don't seem to be interested in it, just calling it junk. That's not true, since we have discovered functions for a number of non-coding elements. There might be even more that we haven't figured out yet. Effects might be less direct (e.g. evolutionary, as mentioned in the answer by Remi.b), but scientist keep working on it. $\endgroup$
    – Frieke
    Commented Feb 27, 2019 at 11:02
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    $\begingroup$ ncbi.nlm.nih.gov/pmc/articles/PMC5570035 $\endgroup$
    – Macond
    Commented Feb 27, 2019 at 23:09

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