What is spandrelism?

In evolutionary biology, a spandrel is a phenotypic feature, a by-product of the evolution of some other traits, rather than a direct product of adaptive selection. That is, possession is a particularly non-advantageous feature, but possession is preserved as it is not particularly harmful.

The term "spandrel" emerged as an architectural word for the roughly triangular space between the tops of the two adjacent arches and the ceiling. When the artists realized that they could design and paint in these small spaces and improve the overall design of the building, these spaces were not used until later.

Stephen Jay Gould and Richard Lewontin brought this term to biology in his 1979 article "the Spandrels of San Marco and Panglossian paradigm: criticism of the adaptationist program", which defined the biological concept and defended the case for a structuralist view of evolution.

 It was invented by Harvard paleontologist Stephen Jay Gould and population geneticist Richard Lewontin in his article "San Marco Spandrels and the Panglossian paradigm: a critique of the adaptationist program" (1979). The evolutionary biologist Günter P. Wagner called the newspaper "the most influential structuralist manifesto".