Read the following passage regarding the evolution of avian flight. Based on the passage, match each researcher or perspective to the statement that most accurately characterizes their view on the development of proto-wings or flight.
The debate over the origin of avian flight has historically been polarized between two camps: the 'arboreal' (trees-down) hypothesis, which posits that flight evolved from gliding arboreal ancestors, and the 'cursorial' (ground-up) hypothesis, which suggests that bipedal, ground-dwelling theropods developed proto-wings to assist in leaping after prey or acting as insect snares, a view famously championed by John Ostrom. Critics of the cursorial model rightly point out the biomechanical improbability of a running animal generating sufficient lift to overcome gravity without already possessing fully formed flight surfaces. Conversely, arborealists like Alan Feduccia argue that true flapping flight could only arise from a gliding intermediate stage, pointing to the energetic advantages of launching from a height.
However, both traditional models mistakenly assume that the primary initial driver for wing evolution must have been directly related to aerial locomotion or leaping. Recent biomechanical research by Kenneth Dial on modern ground birds has introduced a compelling third alternative: wing-assisted incline running (WAIR). Dial demonstrates that developing wings can provide aerodynamic traction, pressing the animal against steep inclines, thus offering an immediate survival advantage before true flight is achieved.
While WAIR elegantly solves the aerodynamic paradox of the cursorial model by providing a functional intermediate stage for proto-wings, it fails to fully account for the initial elongation of forelimb feathers before they could generate any meaningful aerodynamic force. It is far more plausible that these structures initially evolved under the intense pressures of sexual selection for visual display—a function widespread among modern avians. Only once these display structures reached a critical surface area could they be co-opted for aerodynamic functions like WAIR, and eventually, true flapping flight. Thus, the morphological transition to flight was likely a two-stage exaptation, driven first by display and only subsequently by locomotion.
- John OstromForelimb structures initially evolved to confer a predatory advantage to terrestrial bipeds.
- Alan FeducciaThe energetic barriers to achieving flight dictate that early avian ancestors must have launched from elevated environments.
- Kenneth DialIncipient wings provided an intermediate survival benefit by generating aerodynamic forces that aided in ascending steep terrain.
- The AuthorThe initial enlargement of forelimb feathers was driven by social or reproductive pressures rather than direct aerodynamic utility.