Scientists originally applied the term “junk DNA” to any section of DNA that appeared non-functional. Through advances in genomics, the definition has shifted. The term is currently used for a section of the DNA that may have functioned in the past but no longer functions. (See Who Was Adam? for an extensive discussion of the major types of junk DNA—pseudogenes, endogenous retroviruses, SINEs and LINEs—and the mechanisms thought to have generated them.) Because some identical segments of so-called junk DNA occur in a wide range of related organisms (for example, psi GULO in multiple primates), any researchers view it as evidence for the common ancestry of these organisms, a basic tenet of evolutionary theory.
The concept of junk DNA seems to provide strong evidence for an evolutionary model and against a creation model. Such a conclusion assumes, however, that this genetic material really is junk. A growing body of research says otherwise. Biologists and biochemists continue to find evidence of function in every class of junk DNA. It appears that even the quantity of junk DNA in various organisms has been fine-tuned for a purpose. In other words, it serves as evidence for design. Although many scientists still use junk DNA to argue for an evolutionary model, the data seems a close and comfortable fit with a creation model.