In 1979, a biology professor at the University of California Berkeley named Thomas Jukes wrote to Francis Crick, the Nobel laureate and co-discoverer of the helical structure of DNA:
Dear Francis, I am sure that you realize how frightfully angry a lot of people will be if you say that much of the DNA is junk. The geneticists will be angry because they think that DNA is sacred. The Darwinian evolutionists will be outraged because they believe every change in DNA that is accepted in evolution is necessarily an adaptive change. To suggest anything else is an insult to the sacred memory of Darwin.
In his new book What’s in Your Genome?, Laurence A. Moran shows that all the research done in the decades since that letter was written has confirmed what Crick, Jukes, and other specialists believed all along: much of our DNA is indeed a kind of “junk.”
Moran is professor emeritus of biochemistry at the University of Toronto. While he has been a science textbook co-author through five editions of the highly regarded Principles of Biochemistry, What’s in Your Genome? is the first book he has written for the general public. In addition to his teaching duties, Moran has since 2006 run his own blog, “Sandwalk”—named after Darwin’s favorite walking path. Beautifully organized, it’s a comprehensive resource for anyone who wants to learn more about the many complicated aspects of evolution that don’t always get covered in the popular press.
It goes without saying that Moran has tangled with creationists of all stripes for years. Indeed, his blog grew out of the need to carefully defend each and every aspect of the science they attacked. “There is no simple way to explain evolution correctly,” he writes, “but there are many simple ways to explain it badly.”
Moran is not shy about chastising celebrity science authors such as Richard Dawkins who, in Moran’s judgment, ignore or play down the crucial random processes involved in evolution while placing too much emphasis on natural selection and adaptation as the primary drivers of change.
Junk DNA is one of the more complicated examples of how randomness permeates the history of life. Few topics are more misunderstood and deliberately garbled in the press. The evidence that up to 90 percent of the human genome consists of useless DNA, repeatedly copied over the eons alongside all the most important genes that make us who we are, upsets a number of evolutionary biologists who believe—mistakenly, in Moran’s view—that natural selection simply wouldn’t have tolerated the accumulation of so much wasted code. And yet, as Moran shows in eleven detailed chapters, it’s precisely the existence of junk DNA in the genomes of most species that serves as one of the most powerful lines of evidence in support of evolution.
But what exactly do scientists mean by “junk”? First, it’s important to remember what they mean by a gene: a DNA sequence that’s transcribed to produce functional products (proteins) that constitute the body of an organism. Put another way, functional DNA is any stretch of DNA whose deletion from the genome would reduce the fitness of the individual organism (causing illness or death). Junk DNA, by contrast, is any stretch of DNA whose deletion from the genome makes absolutely no difference to the fitness or survival of the individual organism. And it appears we have a lot of it.