Historical-narrative evolutionary explanations for the origin and further evolution of avian feathers involve two steps. The first phase reconstructs a series of probable morphological changes from a reptilian scale to the primitive feather. The second deduces possible functions and biological roles of the features and feasible selective demands on these features at all stages in its evolution. The best explanation for the evolutionary origin of feathers would be one consistent with historical-narrative evolutionary explanations for the origin and further evolution of other features in the history of birds. Feathers of Recent birds have a number of functions and biological roles, and it is difficult to ascertain which of these functions and roles were involved in feather origin. Two major rival published theories are based on the roles of feathers in insulating the body against heat loss and in providing an aerodynamic surface for flight. However, because of the lack of knowledge about the roles and ecological relationships of protofeathers and of the most primitive feathers, it is not possible to test strongly either of these theories, or others as proposed in this symposium, against objective empirical observations to determine which is falsified or is the most probable. Finally it is argued that test of historical-narrative evolutionary explanations, including classifications and phylogenies, is generally difficult to impossible because of the lack of the necessary objective empirical observations.
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Vol. 40 • No. 4