Cross-testing adaptive hypotheses: Phylogenetic analysis and the origin of bird flight

Adaptive scenarios in evolutionary biology have always been based on incremental improvements through a series of adaptive stages. But they have often been justified by appeal to assumptions of how natural selection must work or by appeal to optimality arguments or notions of evolutionary process. Cladistic methodology, though it cannot logically falsify hypotheses of process, provides hypotheses of evolutionary pattern independent of other considerations and so provides a useful test of consilience with genealogy. I illustrate the cross-test of hypotheses of the evolution of several functions and adaptations related to the origin of bird flight with independently derived phylogenetic analysis. Consilience does not support ideas that the close ancestors of birds were arboreal or evolved flight from the trees, nor that they were physiologically intermediate between typical reptiles and living birds, nor that feathers evolved for flight. Rather, the ancestors of birds were terrestrial, they were fast-growing, active animals, and the original functions of feathers were in insulation and coloration.