A large part of this internal mess comes from the endogenous retrovirus. A normal virus works by moving into a host cell and using it to reproduce, but retroviruses reproduce by actually mixing their own genetic material with the DNA of the host cell they're invading. If a normal virus is a home invasion robber, busting down your door and smashing up your stuff, a retrovirus is the creature from Alien, impregnating you with its horrible seed and producing a twisted mockery of everything you once were, and then laughing as that atrocity murders all of your friends. Metaphorically speaking, of course.
In the distant past, retroviruses picked up by our ancestors would occasionally find their way into the sex organs, and the newly virused-up DNA was passed along to their children. As a result of all this virus-laden boning, we modern humans have about 100,000 of these microscopic gate-crashers cluttering up our DNA. When you add in the assorted genetic trash they've left behind, more than 40 percent of human DNA is made up of ancient, sinister and almost certainly cursed viruses.
Scientifically speaking, they are "the clumpy purple thingies."