Final answer:
The principal criticism of the cursorial hypothesis of the origin of flight in birds is that catching insects with feathered hands does not seem practical, suggesting balance and eventual flapping flight as more likely purposes for wing evolution.
Step-by-step explanation:
The principal criticism of the cursorial hypothesis of the origin of flight is that catching insects with feathered hands does not seem practical. The cursorial hypothesis suggests that prehistoric ancestors of birds developed wings while running on the ground, perhaps pursuing prey.
However, wings would have likely evolved not for capturing prey but for balance and eventually flapping flight. This view is contrasted with the arboreal hypothesis, which posits that flight evolved from tree-dwelling creatures that used their feathers for gliding between branches before developing the ability for powered flight. Fossils of creatures like the Archaeopteryx support the latter hypothesis, showing evidence of both gliding capabilities and a tree-dwelling nature.