The liver is the only organ in the body that can regenerate on a massive scale. Did the ancient Greeks—penners of the myth of Prometheus and his “immortal” liver—know this? Hard to imagine how, say medical historians. Human dissection in the ancient Greek world was strictly taboo. Hepatoscopy, the animal-sacrificing/soothsaying tradition practiced in Mesopotamia in that era, focused on the shape and surface of the liver to predict the future, not its innards. And on the battlefield, liver injuries were deadly.
Besides, consider the crowd Prometheus ran with. Athena sprang from Zeus’ head. Dionysus, once shredded to bits by the Titans, completely rebuilt himself around his heart. It only makes sense that Prometheus’ liver was immortal. So was he!
The unparalleled regenerative capacity of the liver was not documented until the late 19th century. (And only in the past few decades has George Michalopoulos’ team begun to reveal how it does so. See p. 24 for that epic tale.) Really, until the 1800s, no one even knew what the liver was for. Humorism—a theory conceived by physician/ philosopher Galen of Pergamon (131-215 ce) in the second century, popularized in the fifth century, and then favored for hundreds of years—held that the liver was the source of our lifeblood and, thusly, our courage. (The proper balance of our bodily fluids was key to maintaining our health as well as our emotions, Galen wrote.) Traces of this hepato-misnomer remain in our language even today. Just ask Yosemite Sam. Or are ya too lily-livered?