Spandrel
A trait or feature that arises as a byproduct of some other process or design rather than being directly selected or intended — like the triangular spaces above an arch that exist only because of the arch's shape.
EverydayConcepts.io
Origin
In 1979, evolutionary biologists Stephen Jay Gould and Richard Lewontin borrowed the architectural term in their influential paper "The Spandrels of San Marco and the Panglossian Paradigm." They argued that the ornate mosaics in the spandrels of St. Mark's Basilica in Venice look purposeful but are really just decorated byproducts of the arches' structure — and that biologists make the same mistake when they assume every trait evolved for a reason.
Updated February 22, 2026