Illustration by Zephyris - GNU Free Documentation License
There's an intriguing article in the Washington Post about remnants of ancient retroviruses found in the human genome. Over the course of evolution, retroviruses like HIV have stitched themselves into human DNA. Clearly, these retroviruses have been defeated by our immune systems, or we would not be around to discuss the matter. However, bits and pieces of these retroviruses remain in our DNA. Kind of like trophies. Indeed, some of the functions provided by these viral skeletons have been hijacked by our immune systems as defenses against incoming retroviruses. Scientists have succeeded in putting the pieces of one retrovirus back together from snippets spread around the genome. Unfortunately, like all such stories, this one starts out interesting, then peters out. There is just too much we don't know or understand about the genome.