Saturday, 2 May 2015

Larry Moran critically reviews "Junk DNA"

Special creationists are desperate to latch onto anything that appears to provide support for their belief that the human genome is not riddled with parasitic DNA, broken genes, and remnants of ancient viral infection, but rather a pristine example of design. One example is Junk DNA, a recently published book by the science writer and virologist Nessa Carey.

Biochemist Larry Moran, who maintains a strong professional and personal interest in the subject of Junk DNA points out why this book will not provide evolution denialists with any support for their position:
"I placed an order for the book and noticed that you can browse the first few pages.  
How bad is it? ... Really bad. She starts out explaining what she means by "junk" DNA. 
There's a bit of linguistic difficulty in writing a book on junk DNA, because it is a constantly shifting term. This is partly because new data change our perception all the time. Consequently, as soon as a piece of junk DNA is shown to have a function, some scientists will say (logically enough) that it's not junk. But that approach runs the risk of losing perspective on how radically our understanding of the genome has changed in recent years 
Rather than spend time trying to knit a sweater with this ball of fog, I have adopted the most hard-line approach. Anything that doesn't code for protein will be described as junk, as it originally was in the old days (second half of the twentieth century). Purists will scream, and that's OK. Ask three different scientists what they mean by the term 'junk', and we would probably get four different answers. So there's merit in starting with something straightforward. 
There are so many errors crammed into these two paragraphs that it would take another book to correct them. Let me just point out that knowledgeable scientists define junk DNA as DNA that doesn't have a function. No other definition is worth the paper it's written on.  
There was never a time when knowledgeable scientists said that all noncoding DNA was junk. Not in the last century, and certainly not in this century. Nessa Carey is not speaking the truth here. I don't think she's lying—although I don't rule out that possibility—but I do think she is seriously mistaken. How in the world could she write a book on junk DNA without learning how the term is defined? 
I also don't think it's correct to say that our understanding of the genome has changed radically in recent years. Mine certainly hasn't and I'm pretty sure that most knowledgeable scientists had a good understanding of genomes 30 years ago. The only exception might be that there are more genes making functional RNAs than we realized back in the 1980s.  
On the other hand, the views of some other scientists have changed a lot. They have learned, to their surprise, that most of our genome is junk and that natural selection has not eliminated all nonfunctional DNA. I don't think that's what Nessa Carey is referring to.  
The debate over junk DNA is not about the existence of junk—that fact cannot be contested. The debate is over the relative amount of junk DNA in various genomes. There's plenty of real, positive, evidence that the human genome has lots of junk DNA (non-functional DNA) but there are still legitimate scientific discussions about the details and there are even debates about possible structural roles for nonconserved DNA (bulk DNA hypotheses). If a journalist is going to write about this stuff, they have to do a lot of homework. This is no place for amateurs. (Emphasis in original)
Those wanting to know what the experts have shown would do well to consult both Ryan Gregory, an expert on genome evolution who maintains a website which frequently comments on junk DNA, not to mention Moran, as well as the evolutionary biologist Dan Graur. Those with some background in biology would do well to consult Michael Lynch's The Origins of Genome Architecture and The Evolution of the Genome, edited by Gregory, or the PNAS paper Footprints of nonsentient design inside the human genome by evolutionary biologist John Avise. As Moran said, this is no place for amateurs, and laypeople interested in this subject need to ensure that they avoid being mislead.