How human would you say you are? if you answered 100 percent (if you bothered to answer at all), you're sadly incorrect. While about 90 percent of your DNA is made of human material, a small percentage of it is considered "alien."
Yes, you are part alien, but not the kind you're thinking of. Sorry, Martian.
About 8 percent of all human DNA is made up of ancient viral fragments hiding deep within the genome.
Viruses are made of RNA (seen as a precursor to DNA, which is more complex). They work to infect their hosts by injecting them with DNA-based replicas of their own RNA.
Because viruses have been doing this for millennia, the fact that some parts of ancient viruses have made their way into the depths of human genetics makes sense.
A recent study in Proceedings of the National Academy of Sciences revealed 19 new pieces of viral DNA in the human genome.
Even freakier, perhaps, is that parts of our bodies have adapted to use these bits of ancient RNA for processes that have to do with fighting disease and increasing fertility.
(via IFL Science)
Now that is the kind of creepiness I can get down with. The human body is home to so much awesome madness.