When visiting Venice in 1978, Gould noted that the spandrels of the San Marco cathedral, while quite beautiful, were not spaces planned by the architect. Rather the spaces arise as "necessary architectural byproducts of mounting a dome on rounded arches." Gould and Lewontin thus defined "spandrels" in the evolutionary biology context to mean any biological feature of an organism that arises as a necessary side consequence of other features, which is not directly selected for by natural selection. Proposed examples include the "masculinized genitalia in female hyenas, exaptive use of an umbilicus as a brooding chamber by snails, the shoulder hump of the giant Irish deer, and several key features of human mentality."