2006/01/01 by KENNETH P. DIAL, Kenneth P. Dial, ROSS J. RANDALL +2 · 15 citations
Earth and Planetary Sciences · Environmental Science · #Paleontology and Evolutionary Biology #Avian ecology and behavior #Fish Ecology and Management Studies
paper · pdf · doi:10.1641/0006-3568(2006)056[0437:wuihaw]2.0.co;2
A s a rebuttal to Darwin's (1859) explanation of the origin and diversification of life, St. George Jackson Mivart (1871) posed a challenge: "What use is half a wing?" With this simple question, Mivart challenged Darwin to explain the adaptive role of intermediate forms within an evolutionary continuum, prompting Darwin to expand on the concept of functional shifts within structural continuity This concept of transitional functional and structural stages is the basis for exaptation, an integral component of modern evolutionary theory A response to Mivart's question is that if the wing of a flying bird is a product of small, gradual structural changes, these transitional forms must have had some function during the evolution of powered flight. But how do we assign and test a hypothetical function or propose an adaptive value for a transitional form that we find preserved only in the fossil record? This dilemma has spurred volumes of publications on the origin of flight, which have characteristically centered around two well-entrenched schools of thought. The first, known as the arboreal theory, proposes that flight evolved from tree-dwelling ancestors and predicts a gliding intermediate phase (Marsh 1880,