Spandrel

An architectural feature common in Renaissance architecture used to support a dome or arch. Often they are decorated, but this decoration is secondary to their structural role.

The term also has an interesting usage in evolutionary biology. In 1979, Stephen Jay Gould conceptualised evolutionary “spandrels”, making the analogy that a trait present in an organism may have arisen as byproduct of some other evolutionary development (e.g. human chins/belly button). This provides an explanation of why biological features might not serve an adaptive function.

Perhaps my favourite example of a biological spandrel is the presence of male-resembling genitalia on female hyenas. This is due to high-levels of androgen which is essential for survival in hyper-aggressive and competitive hyena society.