Fifty years ago James Watson and Francis Crick discovered the structure of DNA. In recent decades, scientists have been puzzled by the fact that approximately only five percent of our DNA codes for the amino acids that create life-giving proteins. The other ninety-five percent that biologists call junk DNA seemed to do nothing at all.

In recent years biologists have begun to realize that this apparently useless DNA may in fact be more than just junk. Researchers at the University of Pennsylvania have shown that within the vast stretches of junk DNA are segments that play an active and possibly harmful role in human evolution. At least seven of these segments, called long intersperse nuclear elements, or L1 elements, can move from one part of the genome to another and insert themselves at various points.

Biologists are still speculating about the roles these mobile L1 elements may play. Some evidence suggests that they act as a sort of repair mechanism, inserting themselves at points on the genome where existing DNA has become damaged. Other studies have shown that L1 elements can also erase existing DNA when they jump to a new location. This can result in significant and often harmful mutations which may have contributed to human genetic diversity.

Since the genetic effects of mobile L1 elements appear to be mainly negative, scientists remain puzzled by their continued existence in the human genome. But as research continues, one thing is certain: junk DNA has emerged from the trash bin of genetic research.