When scientists first began sequencing DNA in the 1970s, they noticed something strange: along the familiar double-helix were small pieces of DNA that coded for particular proteins, followed by long strings that appeared to do nothing at all. The human genome, in other words, was mostly fluff.

But like the bolts left over after assembling an IKEA dresser, it turns out that much of this so-called junk may serve a purpose. Over time, some scientists started to suspect that certain strings of DNA had once been junk, but evolved the ability to code for proteins. And in 2012, a research program called ENCODE found that around 75% of junk DNA undergoes transcription (the first step to a gene actually being expressed). However, not all scientists agree that this removes their "junk" status, since that doesn't necessarily mean that they have any biological function.

The fact that our genome isn't an orderly chain of useful genes, but instead a heap of useful, halfway useful, and totally useless strings of DNA is yet another bit of evidence for the fact that we evolved, and weren't designed. Evolution works blindly through random mutations that sometimes kill off a species and sometimes help it survive, and as a result it leaves behind useless mutations that just stay put over the millennia. To call so much of your DNA junk might sound like a bad thing, but think of it this way: it's just a genetic keepsake from generations of evolution.