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 traits or behaviors not because they are directly adaptive, but because they happen to appeal to an existing preference in the opposite sex. Let me give you two examples. First, consider the swordtail fish. Female swordtails have a pre-existing preference for males with a longer tail, because it resembles a food source they already like. Over time, males evolved an elongated sword-like tail to exploit this bias, even though it makes swimming less efficient. Second, think about the bowerbird. Females are naturally attracted to the color blue, possibly because it signals the presence of berries or water. Male bowerbirds decorate their nests with blue objects—flowers, feathers, even plastic—to trigger this preference, despite the fact that the blue items provide no direct benefit to the female or the offspring. In both cases, the trait is not about survival or direct fitness, but about tapping into a sensory bias that already exists.