I loosely follow the prescription of Adolph Seilacher (1970, 1973, 1979), who coined the term constructional morphology, to argue that form in organisms evolves under the combined influence of

1. How a structure might be formed by nature of the materials (and, I would add, developmental scheme)

2. Phylogenetic origin, meaning the ancestral character states belonging to immediate ancestors, and

3. Adaptation, as guided by natural selection

This spirit of this very reasonable explanation of phenotypic evolution is also to be found in Jacob's (1983) idea of tinkering, which admits to the eccentric history of evolutionary pathways and co-optation of structures for new functions. The extremists (e.g., Gould 1997), however, would have us believe that nonadaptive aspects of form have been woefully neglected. They claim that evolutionary biologists have sought adaptive explanations in every structure they encounter, to the extent that the structures are perfectly shaped by evolution to perform a function in the very best way possible (Gould and Lewontin 1979; Lewontin 1978). This point of view is a misunderstanding of typical biological practice, fueled by an overly idealized view of biological science. It is true that when seeing a structure for the first time, nearly all biologists ask: “What does this do?” Thus has the function of so many previously mysterious structures (e.g., islets of Langerhans, Golgi bodies) been eventually discovered. Such an approach is surprisingly conserved in all areas of biology, from the subcellular to the whole organism (e.g., what does the springlike backbone of the cheetah do?). That is because it has been so universally successful.