Jonathan Wells will publish The Myth of Junk DNA early in May, 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? My mom loves those.
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 the failure to admit an error in this case?
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?
In a word, evidence. The first to emerge was the fact that almost all of an organism’s DNA is transcribed into RNA. (So although most of it may be non-protein-coding, it codes for RNA.) From a Darwinian perspective, this is surprising: Why would an organism struggling to survive devote so many of its internal resources to producing supposedly useless RNA? Indeed, since 2003 it has become clear that non-protein-coding RNAs perform many essential functions in living cells.
Pseudogenes constitute one type of so-called “junk DNA.” These are segments of DNA that resemble segments that elsewhere (or in other organisms) code for protein. Yet RNAs transcribed from some pseudogenes have been found to function in regulating how much protein is produced by the DNA segments they resemble. Repetitive DNA, in which a non-protein-coding sequence is repeated many times, is another type of so-called “junk DNA.” Yet repetitive DNA is now known to regulate many essential functions, including embryo implantation in mammals.
There is also growing evidence that non-protein-coding DNA can perform functions that are independent of its sequence. One example is the region of a chromosome (called a “centromere”) that attaches it to other structures in the cell. Another example is the retina in the eyes of nocturnal mammals, in which non-protein-coding DNA acts like a liquid crystal to focus scarce rays of light.
Some claim that ID theorists predicted the finding and others claim they didn’t. What’s your take?
The literature doesn’t lie. Design theorist William A. Dembski wrote in 2004, “For years now evolutionary biologists have told us that the bulk of genomes is junk and that this is due to the sloppiness of the evolutionary process. That is now changing. For instance, researchers at the University of California at San Diego are finding that long stretches of seemingly barren DNA sequences may form a new class of noncoding RNA genes scattered, perhaps densely, throughout animal genomes. Design theorists should be at the forefront in unpacking the information contained within biological systems.” (The Design Revolution, p. 317.) At the time, biologists such as Dawkins, Coyne, Avise and Collins were still claiming that most of our DNA is junk.
Do you think this will change the Darwinism vs. ID debate in any way? If not, why not? If so, how?
To the extent that evidence matters, new discoveries of functions in non-protein-coding DNA will affect the debate. Unfortunately, many people embrace Darwinian evolution because of an a priori commitment to materialistic philosophy. For them, nothing can challenge that commitment, so they spend much of their time explaining the evidence away. Ironically, many such people reject ID on the grounds that no evidence can possibly count …, but they also say that the evidence proves ID is false. Obviously, evidence will not persuade such people.
Your other books have been dissections of the various Darwin myths. I am thinking of Icons of Evolution and Politically Incorrect Guide to Darwinism and Intelligent Design. Is this like that or is it different? If so, how?
Chapter 2 of my new book is titled “Junk DNA: The Last Icon of Evolution?” Unlike the icons I dissected in Icons of Evolution, junk DNA is not a visual image, but it’s an icon of evolution nevertheless—meaning that it is embraced and defended for theological and philosophical reasons, not because of the evidence. Like Haeckel’s faked embryo drawings and staged photos of peppered moths, junk DNA is not science, but myth.
Can you interpret this for me, from Larry Moran (University of Toronto evolutionary biologist): “I don’t demand civility, but I do demand accuracy. When Denyse and her friends say that Darwinists promoted junk DNA I have to draw the line.” But he must be referring to my observation that originated in Francis Collins’s (US government’s chief 2000 genome mapper’s [!]) statements in a well-received and widely read book. Are there two types of truths at work here? Evidence, and … what?
When I use the term “Darwinist,” I mean someone who accepts and defends the theory I describe in my answer to Question 2. Crick and Orgel were Darwinists in this sense; so are Miller, Dawkins, Coyne, and Avise—all of whom have promoted the myth of junk DNA. When Collins published The Language of God in 2006, he not only promoted junk DNA but also wrote that “Darwin’s theory of evolution, that is, descent from a common ancestor with natural selection operating on randomly occurring variations” is “unquestionably correct” (pp. 127, 141). Sure sounds like a Darwinist to me.
Collins also wrote that intelligent design is a “God of the gaps” position that is doomed to collapse with further advances in science (p. 193). But Collins has it exactly backwards: He and other promoters of the myth of junk DNA have put their faith in a “Darwin of the gaps” argument that must now retreat in the face of new advances in genome research.
Okay, everyone, back to work tomorrow in Darwinworld, where facts like these do not matter in the least.