24 December 2007

Talking trash about "junk DNA": Introduction

"Junk DNA" is a very popular subject among anti-evolution commentators. At the Discovery Institute (DI) and Reasons To Believe (RTB), as well as other creationist outlets, you can find ample discussion of "junk DNA" and why it matters to Christians who don't like evolution.

I've mentioned this topic several times myself, because I believe that the misuse of science by creationists is seldom more in evidence than when opponents of evolution confront genetics and genomics. As I've noted before, common descent provides a superior explanation for the extraordinary facts gleaned through comparative genomics (i.e., the examination and comparison of genome structure, overall and in detail, among different types of organisms), and there is no competing scientific explanation. As I see it, a knowledgeable Christian person considering these data has exactly two rational alternatives: 1) acknowledge the explanatory power of common ancestry and accept its reality; or 2) acknowledge the appearance of common ancestry but deny its reality. Any other choice is indicative of ignorance or of some form of intellectual dishonesty; I have advocated the use of the concept of folk science to account for the tendency of some apologists (e.g., the "scholars" at Reasons To Believe) to misrepresent science in defense of their preconceived interpretive framework.

Regarding so-called "junk DNA," the claims of the DI and RTB are quite similar, and I will consider them together here.

My assertion in these next 3 posts on "junk DNA" is this in a nutshell: the writing of the DI and RTB on the subject of "junk DNA" is a melange of half-truths, non sequiturs, quote-mined proof texts and outright fabrications that adds up to one of the clearest examples of folk science that I can imagine. My conclusion is that one would be very unwise to consult these sources for knowledge about developmental or evolutionary genetics, and that the architects of this deception are engaged in scholarly misconduct if not outright dishonesty.

When these apologists write about "junk DNA," they commit sins of commission and omission. I've identified 3 significant themes in this edifice of folk science, and the 3 posts will deal with each in turn.

  1. Creationists insist that "junk DNA" is functional and therefore that evolutionary claims regarding its origin are mistaken.
  2. Creationists systematically ignore fact and theory regarding the nature of vast numbers of non-coding genetic elements, which make up the bulk of the genetic material that is referred to as "junk DNA." Specifically, these apologists ignore (and sometimes deny) the fact that millions of chunks of DNA in the human genome alone are known to be mobile genetic elements.
  3. Creationists distort the nature of ongoing research and debate concerning the evolutionary roles and fates of various "junk DNA" elements.
I'll deal with these 3 themes in 3 upcoming posts, but here are some teasers.

Creationists of various stripes commonly claim that because evolutionary biologists automatically assumed that non-coding DNA lacked function, little or no research on the subject occurred for decades. That claim is doubly false: biologists have always adopted various stances on the functional roles of non-coding DNA, and consequently research into its function has proceeded apace.

Enormous numbers of DNA elements that make up the bulk of the human genome -- and most of its non-coding "junk" segments -- have been identified and are being actively investigated by molecular biologists. These elements are anything but mysterious: they are so-called mobile genetic elements of various kinds, with well-known properties. Their properties, and their use in scores of analyses of evolutionary relationships, are systematically omitted from creationist writings on the subject.

The proteins that enable animals to smell are called olfactory receptors (ORs). The human genome contains about 800 OR genes, but more than half of them have been inactivated by mutation, yielding what are called pseudogenes. These "fossil genes" are found in precisely the same locations within the genome as are the fully-functional versions in other mammals (i.e., mice). Analysis of these genes and their properties has led to the construction of a highly coherent explanatory framework that accounts for the existence of these pseudogenes and the evolution of smell in vertebrates. Looking for a creationist approach to these data? The word 'olfactory' appears nowhere on RTB's website; at the DI, you'll find it in lots of articles...about stem cells.

So, stay tuned, or if you just can't wait go to Genomicron, a superb blog about nothing but genomes and evolution.

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