χίμαιρα

Greek chímaira means 'young she-goat.' The mythological Chimera — a creature with a lion's head, a goat's body, and a serpent's tail, breathing fire from the goat head — was named after its middle section. Why the goat and not the lion or the serpent was chosen for the name is unclear. Homer describes the Chimera in the Iliad (Book VI, line 179): 'a thing of immortal make, not human, lion-fronted and snake behind, a goat in the middle, and snorting out the breath of the terrible flame of bright fire.' Bellerophon, riding Pegasus, killed it.

The Chimera of Arezzo — an Etruscan bronze sculpture from approximately 400 BCE, discovered in 1553 — is one of the finest surviving examples of Etruscan art. It depicts the Chimera in its final moment, wounded by Bellerophon's lance, with the goat head screaming and the serpent tail coiling. Cosimo I de' Medici acquired it and displayed it in his palace. Giorgio Vasari restored it. The sculpture helped define the Renaissance understanding of the ancient myth.

In genetics, a chimera is an organism containing cells from two or more genetically distinct sources. Chimerism occurs naturally: some fraternal twins absorb cells from each other in the womb, creating individuals whose blood cells have one DNA profile and tissue cells have another. Human-animal chimeras — organisms with both human and animal cells — are being created in laboratories for organ transplant research. In 2017, scientists at the Salk Institute grew human cells in pig embryos. The mythological hybrid has become a biological reality.

The word chimera in everyday English means 'an impossible fantasy' or 'a wild illusion.' To call something 'chimerical' is to say it cannot exist. The irony is precise: the word for a creature that could not exist is now the scientific term for an organism that very much does exist. The impossible became the actual. The she-goat became the future of medicine.