Not long ago, you learned that many of the basic processes of human life require a partnership between your body and the bacteria that calls it home. Now you’re ready to learn another disturbing truth: you have an even more intimate relationship with viruses.
The key players are retroviruses, a broad class of viruses that carries strands of RNA instead of DNA. The interesting and highly technical part is that your body sometimes converts RNA back into DNA. As a result, a virus that holds a piece of RNA is able to fuse itself into your genes, altering your genetic code.
Before you panic, remember that your body has trillions of cells, and virus-infected cells generally don’t last long before white blood cells destroy them. However, there’s always the possibility that a virus will find its way into a germ-line cell—in humans, these are the cells that produce male sperm and female egg. If a virus lands in one of these cells, it has a good shot at being incorporated into the genes of the next generation. And that’s not science fiction, as recent studies suggest that nearly 10 percent of human DNA consists of pasted-in viruses from the past.
Now, it’s important to understand that a virus integrated this way probably isn’t going to infect newly minted babies. That’s because the virus incorporates its DNA in a random place. Usually, it’s in the vast wasteland called junk DNA—segments of your genetic code that don’t appear to do anything at all. However, occasionally a virus lands somewhere important, and the result is usually trouble. Some researchers believe hemophilia and muscular dystrophy are two genetic diseases that cropped up when random, viral DNA blundered into the wrong spot.
Finally, here’s the really interesting part: As you probably know, evolution works when apparently random changes in a creature’s DNA give it a valuable survival advantage. And while viral DNA is more likely to cause a problem than to confer a benefit (and is most likely to do nothing at all), every once in a while a bit gets into a place where it just might do real good. In fact, many scientists believe that viruses have helped shape evolution on our planet by reshuffling genes, pasting in their own contributions, and carrying genes from one species to another. So while life started as mere bacteria, viruses just might have supplied some of the variety that drove evolution forward and led, eventually, to the creation of you.
Source of Information : Oreilly - Your Body Missing Manual