托福口语 Task 4

Today, we're going to talk about a fascinating behavioral adaptation in animals called 'sensory bias.' Sensory bias refers to the idea that certain signals or traits in animals evolve not because they are directly beneficial for survival, but because they happen to appeal to pre-existing sensory preferences in the opposite sex. Let me give you two examples. First, consider the swordtail fish. Female swordtails have an innate preference for males with longer tails, even though longer tails make swimming more difficult. Researchers found that this preference likely evolved because females are naturally drawn to any elongated appendage—a sensory bias that predates the ornament itself. In fact, females even prefer artificial models with elongated tails. Second, think about the bowerbird. Male bowerbirds build elaborate structures decorated with blue objects. This isn't because blue signals good genes, but because female bowerbirds have a natural visual sensitivity to blue, likely linked to their foraging for blue fruits. So, males exploit this pre-existing visual preference to attract mates. Both examples show how sensory systems can drive the evolution of exaggerated traits.