Okay -if you are reading, could whoever told me about spandrels pipe up. It's been resonating with my urban/suburban photography ever since, but I can't remember who first mentioned it to me...
"Dr. Gould and Dr. Richard Lewontin soon elaborated on the importance of how organisms are built, or their architecture, in a famous paper about a feature of buildings known as a spandrel. Spandrels, the spaces above an arch, exist as a necessary outcome of building with arches. In the same way, they argued, some features of organisms exist simply as the result of how an organism develops or is built. Thus researchers, they warned, should refrain from assuming that every feature exists for some adaptive purpose."
There are four or five accepted and cognate meanings of spandrel in architectural and art history, all relating to the space between a curved figure and a rectangular boundary — such as the space between the curve of an arch and a rectilinear bounding moulding, or the wallspace bounded by adjacent arches in an arcade and the stringcourse or moulding above them, or the space between the central medallion of a carpet and its rectangular corners."
"In the context of evolution, a spandrel is a metaphor for characteristics that are or were orginally side effects and not true adaptions to the environment. This metaphorical meaning works no matter which kind of architectural spandrel is referred to: the spandrel is the un-designed gap between other features, which is then often exploited for a use of its own."