Jonathan Wells has just published The Myth of Junk DNA, and offers answers to some questions posed by Denyse O’Leary:
So, for those who dropped science after Grade Ten, what is junk/non-coding DNA?
“Non-coding” in this context means “non-protein-coding.” An important function of our DNA is to specific the sequences of subunits (amino acids) in the proteins that (along with other types of molecules) make up our bodies. When molecular biologists discovered in the 1970s that about 98% of our DNA does not code for proteins, some biologists called non-protein-coding DNA “junk.”
Why was it called “junk” in the first place? And why does all this remind me of one of those auction program episodes where someone is storing leftover carpet nails in what turns out to be a Ming dynasty vase?
According to Charles Darwin’s theory, all living things are descendants of common ancestors that have been modified solely by unguided natural processes that include variation and selection. In the modern version of his theory—neo-Darwinism—genes control embryo development, variations are due to differences in genes, and new variations originate in genetic mutations. In the 1950s, neo-Darwinists equated genes with DNA sequences (Francis Crick called DNA “the secret of life”) and assumed that their biological significance lay in the proteins they encoded. The 98% of our DNA that does not code for proteins was attributed to molecular accidents that have accumulated in the course of evolution.
“The amount of DNA in organisms,” neo-Darwinist Richard Dawkins wrote in 1976, “is more than is strictly necessary for building them: A large fraction of the DNA is never translated into protein. From the point of view of the individual organism this seems paradoxical. If the ‘purpose’ of DNA is to supervise the building of bodies, it is surprising to find a large quantity of DNA which does no such thing. Biologists are racking their brains trying to think what useful task this apparently surplus DNA is doing. But from the point of view of the selfish genes themselves, there is no paradox. The true ‘purpose’ of DNA is to survive, no more and no less. The simplest way to explain the surplus DNA is to suppose that it is a parasite, or at best a harmless but useless passenger, hitching a ride in the survival machines created by the other DNA.” (The Selfish Gene, p. 47)
Since the 1980s, however, and especially after completion of the Human Genome Project in 2003, biologists have discovered many functions for non-protein-coding DNA. If the Ming vase is a living cell and the leftover carpet nails are “junk DNA,” it turns out that the nails are not only made of gold, but they also make an essential contribution to the beauty of the vase.
Interestingly, in the “nail dump is Ming vase” story, no one insists that nobody ever thought it was just another piece of junk. [They almost always say, “Yes, we thought so but had no idea …”] So what’s behind that?
Some people revise history by claiming that no mainstream biologists ever regarded non-protein-coding DNA as “junk.” This claim is easily disproved: Francis Crick and Leslie Orgel published an article in Nature in 1980 (284: 604-607) arguing that such DNA “is little better than junk,” and “it would be folly in such cases to hunt obsessively” for functions in it. Since then, Brown University biologist Kenneth R. Miller, Oxford University biologist Richard Dawkins, University of Chicago biologist Jerry A. Coyne, and University of California–Irvine biologist John C. Avise have all argued that most of our DNA is junk, and that this provides evidence for Darwinian evolution and against intelligent design. National Institutes of Health director Francis Collins argued similarly in his widely read 2006 book The Language of God. It is true that some biologists (such as Thomas Cavalier-Smith and Gabriel Dover) have long been skeptical of “junk DNA” claims, but probably a majority of biologists since 1980 have gone along with the myth. The revisionists are misinformed (or misinforming).
What caused the change of view about junk DNA? Can you suggest a couple of key findings?
Denyse O'Leary is co-author of The Spiritual Brain.