Here's an excellent question from a reader:
How did the ancients know that the liver regenerates (as demonstrated by the Prometheus myth?)
And in ineluctable, painful bonds
Zeus fastened Prometheus
of the subtle mind, for he drove a stanchion
through his middle. Also he let loose on him the wing-spread eagle,
and it was feeding
on his imperishable liver, which by night
would grow back
to size from what the spread-winged bird
had eaten in the daytime.
Hesiod, Theogony, lines 522-525 (translation R. Lattimore)
Someone who knows more about Greek medicine might be able to tell whether the ancient Greeks did know that the liver regenerates-- or whether Hesiod's story is a lucky guess. To me, they must have known, if only because battle wounds give doctors a wealth of observational knowledge. But we have lost many times more ancient medical knowledge than has been preserved in surviving manuscripts. I don't doubt there were plenty of ancient hepatologists who could answer this question.
I'll confess a torn liver makes me queasy, even though now we have miraculously found a way to transplant part of a liver into a needy recipient and have both parts (donor's and recipient's) regenerate. I'm more interested in the fact that Prometheus had a liver at all.
The Olympian gods are anthropomorphic-- that is, in the shape of people-- but the Greeks didn't consider their default physiology to be human. Zeus' natural appearance was as a thunderbolt, as Semele, the mother of Dionysus, found out too late. The gods' food and drink was ambrosia and nectar, respectively. Ambrosia literally means "immortal stuff." The gods, though they liked to sniff the smoke of sacrificed animals, had no need of human food. Shouldn't they therefore lack human organs?
The ancient Greeks followed their own logic, however. That Prometheus had a liver shows his close connection with mortals. This makes sense, because he is generally considered a helper of humans, and in later literature, a creator of them.
But Hesiod himself is quick to point out that the liver is special-- the property of divinity. Richmond Lattimore, a brilliant translator, calls Prometheus' liver "imperishable." The Greek word is athanaton, which means "immortal" or "not subject to death." Hoi athanatoi, "the immortals," is a common synonym for the gods. So whether Hesiod knew that the liver regenerates or not, he makes it into a super-quick regenerating organ to underline that Prometheus was indeed athanatos-- undying.
Prometheus shares humans' suffering through his vulnerable liver, and at the same time is distanced from them because of the organ's special characteristic. This distance and proximity between gods and humans is a hallmark and a paradox of Greek mythological thought, a paradox that is never resolved in that nation until the theology of the fully human, fully divine Jesus develops in Christianity.
Consider the Hittite (central and southwest Turkey, second millennium BC) idea of divinity, in contrast to the Greek. These gods were more fully anthropomorphic than the immortals on Olympus. They depended on food offerings from the great king, who in turn held a kind of divine status, and was immortalized after his death.
There may be a papyrus out there still to be discovered in the Egyptian sands-- or in a dusty drawer at Duke University-- which tells us how the Greeks found out that the liver regenerates. But until then, Hesiod's ingenious story provides us plenty of onions for seasoning the question.