completely unrelated to the post but im obsessed w ur metaphorical use of the word spandrel. i had not encountered it before. fascinating
Oh! Sorry, it's a reference to Stephen Jay Gould and Richard Lewontin's famous paper "The Spandrels of San Marco and the Panglossian Paradigm." Essentially, what Gould is doing is using the spandrel—an architectural term—as a metaphor for a body part.
This is a spandrel:
It's the little bit on the side of an arch in a cathedral. They're often decorated heavily with art patterns in their own right, but they exist as a byproduct of the need for an arch, not as ornamental pieces in their own right: although their decorations can be meaningful aesthetically, their existence isn't driven by the need for aesthetics.
My favorite example of a human spandrel in this sense is the philtrum: the groove running down the upper lip from nose to mouth. People have invented all kinds of functions as reasons for the philtrum to exist, like a groove for mucus to flow through. But it's probably simply a byproduct of the way that the cranium develops during gestation, a split tube coming around together and fusing to create the face and jaws.
It's a very good paper, and I think everyone should read it because it makes some extremely important points about understanding systems and making inferences about the functional origin of moving parts.
