a spandrel is a triangular space which exists over the haunches of an arch. Spandrels—more often called pendentives in this context—are found particularly in classical architecture, especially Byzantine and Renaissance churches. 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." In Voltaire's Candide, Dr. Pangloss is portrayed as a clueless scholar who, despite the evidence, insists that "all is for the best in this best of all possible worlds". Gould and Lewontin asserted that it is Panglossian for evolutionary biologists to view all traits as atomized things that had been naturally selected for, and criticised biologists for not granting theoretical space to other causes, such as phyletic and developmental constraints. The relative frequency of spandrels, so defined, versus adaptive features in nature, remains a controversial topic in evolutionary biology. An illustrative example of Gould's approach can be found in Elisabeth Lloyd's case study suggesting that the female orgasm is a by-product of shared developmental pathways. Gould also wrote on this topic in his essay "Male Nipples and Clitoral Ripples," prompted by Lloyd's earlier work. Gould was criticized by philosopher Daniel Dennett for using the term spandrel instead of pendentive, a spandrel that curves across a right angle to support a dome. Robert Mark, a professor of civil engineering at Princeton, offered his expertise in the pages of American Scientist, noting that these definitions are often misunderstood in architectural theory. Mark concluded, "Gould and Lewontin's misapplication of the term spandrel for pendentive perhaps implies a wider latitude of design choice than they intended for their analogy. But Dennett's critique of the architectural basis of the analogy goes even further astray because he slights the technical rationale of the architectural elements in question." Evolutionary progress Gould favored the argument that evolution has no inherent drive towards long-term "progress".