托福口语 Task 4

Today, we're going to talk about a fascinating behavioral adaptation in animals called 'sensory bias.' This occurs when a trait evolves in one context—say, for survival—and later gets co-opted for another function, like mating. Let me give you two clear examples. First, consider the swordtail fish. Females of this species have a natural preference for males with longer tails. Why? Because a longer tail improves swimming agility, helping the fish escape predators. Over time, females associated the longer tail with better survival skills, so they began choosing males with longer tails as mates. Second, think about the bowerbird. Male bowerbirds build elaborate structures called bowers decorated with blue objects—berries, feathers, even plastic. Females visit these bowers to choose a mate. Research shows that the color blue is highly visible in the dim forest understory, making it easier for females to spot predators while inspecting the bower. So, a preference for blue decorations likely started as a survival advantage, and later became a signal of male quality in mating.