托福口语 Task 4

Today we're going to talk about a fascinating concept in animal behavior called 'sensory bias.' This is the idea that animals develop certain behaviors not because they are adaptive in themselves, but because they happen to exploit pre-existing sensory preferences in the opposite sex. In other words, a trait or behavior becomes attractive simply because it triggers a response that already exists in the female's brain. Let me give you two examples to illustrate this. First, consider the swordtail fish. Female swordtails naturally prefer males with longer tails, even though the tail itself doesn't help the male survive or find food. This preference is thought to originate from the females' natural attraction to larger, more visible objects—a bias that predates the evolution of the long tail. So males with longer tails are simply exploiting that existing preference. Second, take the case of certain birds, like the bowerbird. Males build elaborate structures—bowers—decorated with blue objects. Experiments show that females are inherently drawn to the color blue, likely because it signals food, like ripe berries, in their environment. The males' blue decorations tap into this pre-existing attraction, making the male more appealing. So in both cases, the behavior or trait is not new; it just triggers an ancient sensory response.