Planet Earth might be home sweet home, but is it really humanity's birthplace? We explore science fiction stories where humans come from everywhere but Earth, be it by colonization, alien experiments, or good old-fashioned panspermia.
Panspermia is the term for the most scientifically plausible version of this concept, but it isn't necessarily what science fiction usually presents. The panspermia hypothesis holds that the building blocks of life are not found exclusively on planetary bodies but are instead found scattered throughout the cosmos, and it is these spaceborne particles that are at least partly responsible for life on Earth. There's a little circumstantial evidence for the theory (although far, far more to support the reliable old "Life comes from Earth" hypothesis), and there is something undeniably fascinating about the subtext – the aliens are already here, and we are they. But science fiction barely ever depicts the actual theory of panspermia, mostly because it's just a physical process that takes billions of years to play out and is pretty boring unless you're willing to get really mystical.