Read the passage below and match each scholarly viewpoint or section (Left Column) with its specific structural role in the overall development of the passage's argument (Right Column).
For over a century, evolutionary biologists examining the origin of avian flight divided sharply into two camps. Proponents of the cursorial ("ground-up") hypothesis maintained that flight evolved in bipedal, terrestrial theropods that used rapid running and flapping forelimbs to generate lift. Conversely, advocates of the arboreal ("tree-down") hypothesis contended that flight originated when tree-dwelling ancestors used primitive feathered limbs to parachute or glide between branches, gradually acquiring powered flapping.
This long-standing binary was challenged by Kenneth Dial’s formulation of Wing-Assisted Incline Running (WAIR). Dial demonstrated that living gallinaceous birds utilize flapping forelimbs not to produce lift, but to generate aerodynamic traction, pressing their bodies against steep inclines to run up surfaces otherwise inaccessible. By framing early wing movements as aids to terrestrial locomotion rather than flight per se, WAIR reconciled elements of both classical models while bypassing the aerodynamic implausibilities inherent in pure cursorial lift.
Recently, functional morphologists have advocated an integrative framework that incorporates WAIR into ontogenetic and ecological contexts. Rather than viewing cursorial, arboreal, and WAIR dynamics as mutually exclusive pathways, this modern synthesis suggests that proto-avian lineages utilized distinct behavioral strategies depending on developmental stage and terrain complexity. Consequently, the debate has shifted from declaring a single origin mechanism to analyzing how multifaceted physical constraints shaped forelimb evolution across varied microenvironments.
Which of the following correctly matches each viewpoint or section with its structural role in the passage?
- Cursorial Hypothesis ("Ground-up" model)Serves as one of two original opposing paradigms, positing that flight originated in ground-running theropods generating aerodynamic lift during sprinting.
- Arboreal Hypothesis ("Tree-down" model)Serves as one of two original opposing paradigms, asserting that flight originated from tree-dwelling organisms gliding down between branches.