托福口语 Task 3

In biology, organisms often develop traits that appear to be beneficial but are actually not shaped by natural selection for their current function. This is known as an exaptation. An exaptation is a feature that originally evolved for one purpose, but later becomes co-opted for a different, often unrelated, use. Unlike adaptations, which arise directly due to selective pressure for a specific function, exaptations are pre-existing structures or behaviors that acquire new roles, sometimes dramatically altering the organism's evolutionary trajectory.

Professor: Think about the feathers of modern birds. For a long time, scientists thought feathers evolved for flight. But fossil evidence shows that some dinosaurs, like the small theropods, had simple, downy feathers long before any creature could fly. These early feathers likely served for insulation—keeping the animal warm, or maybe for display to attract mates. So, they evolved for warmth or show. Later, when some of these dinosaurs' descendants—the early birds—began to glide or flap, those same feathers became longer, stiffer, and asymmetric. They were then co-opted for a new function: generating lift for flight. So feathers are not an adaptation for flight; they are an exaptation. Their original purpose was insulation or display, but they later became crucial for aerial movement.