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The assertion that the human genome consists largely of "junk" DNA was made by scientists beginning in the early 1970's when they began to realize that a lot of DNA was not coding for proteins, about the only thing scientists thought DNA was good for at that time. Why there would be so much DNA (up to 95% or more of DNA) that was not making up the protein coding portion of the genome was perplexing to some, and to cover their ignorance, scientists coined the word "Junk DNA" to refer to the mass of DNA that was not coding for proteins. For example Stephen Gould remarked:

Our 30,000 genes make up only 1 percent or so of our total genome. The rest - including bacterial immigrants and other pieces that can replicate and move - originate more as accidents of history than as predictable necessities of physical laws. Moreover, these noncoding regions, disrespectfully called "junk DNA," also build a pool of potential for future use that, more than any other factor, may establish any lineage's capacity for further evolutionary increase in complexity. S. Gould, New York Times, Feb 19, 2001

 The choice of this term is unfortunate, because it implies the DNA is non-functional, and thus uninteresting. As subsequent investigation has shown, this term probably delayed the investigation of that DNA for decades.

More recently, Wojciech Makalowski summarizes the current thinking about "Junk DNA":

"“Although catchy, the term ‘junk DNA’ for many years repelled mainstream researchers from studying noncoding DNA. Who, except a small number of genomic clochards, would like to dig through genomic garbage? However, in science as in normal life, there are some clochards who, at the risk of being ridiculed, explore unpopular territories. Because of them, the view of junk DNA, especially repetitive elements, began to change in the early 1990s. Now, more and more biologists regard repetitive elements as a genomic treasure ( 4, 5).” (Wojciech Makalowski, “Not Junk After All,” Science, Vol. 300(5623): (May 23, 2003). )

We now recognize that some of the most important aspects of what living cells do is encoded in the "Junk DNA" and it is the object of intensive scrutiny. Today, the term is almost never used except with reference to past usages. Molecular biologists realize that whatever the mass of the DNA is doing, it is not "Junk."

______________________________________________________ Ó 2010 Arthur V. Chadwick, Ph.D.