Junk DNA, which accounts for almost half of the human genome, was originally believed to have no purpose. However, it is now emerging that movement of junk DNA, in a cut-and-paste mechanism, can lead to beneficial changes in cells.
The term "junk" DNA, of course, derives from the evolutionary view that life is a fluke. The most complex structures known, which no one could have imagined, just arose on their own. And when evolutionists can't imagine how something works, then they label it "junk."
They might be right sometimes, but so far quite a bit of "junk" has been found to be functional. Even some of the "junk" DNA is turning out to be important.