If you’re familiar with the word “chimera,” it’s probably from Greek mythology, where it refers to a fire-breathing, three-in-one monster — lion-like overall, with a goat’s head protruding from its back and a snake’s head at the tip of its tail.
The modern, scientific worldview leaves little room for these grotesque creatures, but it has replaced them with something just as strange and wonderful: human chimeras.
Most of us are the product of a single genetic code. When our parents conceive us, their chromosomes combine to form the unique sequence of DNA that we carry with us for the rest of our lives. Under the right circumstances, however, it's possible for one body to contain two distinct genomes.
Borrowing from the Greeks, scientists call this condition chimerism. It isn’t typically a health concern, and it won’t cause horns or extra heads to sprout from inconvenient locations. You’d never know someone was a chimera simply by looking at them. That said, the condition can put unwitting chimeras in bizarre situations, and it’s more common than you’d expect. In fact, there’s a decent chance you could be one yourself.
