The late American palaeontologist Stephen Jay Gould wrote a lot about passive strategies within evolution. He used the architectural term “spandrel” to refer to a byproduct of adaptation that is not necessarily adaptive in itself.
Spandrel characters appear subsequently as co-opted by-products. An example is in the extinct Irish Elk. It had a hump at its shoulders, seen in cave-paintings and interpreted from fossils. The hump had no known function, like the vestigial appendix –
Also in Ireland many bare walls of houses are used for political paintings. Such space assumes the character of a spandrel.
It is an art-form that has evolved its own genre: