In many of his essays, Steven J. Gould has suggested complications or revisions to any simple version of the Neo-Darwinian synthesis. (see, for example Wonderful Life, an graphic account of some contingencies of natural history -- as opposed to any predictable, progressive process) He has also proposed a number of alternative concepts to simple adaptation. In "The Spandrels of San Marco and the Panglossian Paradigm," ( Proceedings of the Royal Society of London , 205, 281-288) Gould and Lewontin warned against "naive adaptationism" in the explanation of traits that had emerged for other reasons. Using the dome and spandrels of the basilica of San Marco as an illustration, Gould and Lewontin showed that some traits have no specific function, but are present for reasons of architecture, development, or history. The triangular spaces of the spandrels at San Marco are simple solutions to the problem of filling in the spaces left by placing a dome on four arches. In themselves, they should not be called adaptations, as they serve no function on their own. (but they may become part of a "Bauplan.")
In another paper, ("Exaptation -- a missing term in the Science of Form" Paleobiology, 8, 4-15) Gould and Vrba use the term Exaptation to describe the new use of parts that were originally adapted to some other function or of spandrels that had no function at all.