Аудирование TOEFL

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Listen to part of a lecture in a biology class. The professor is discussing animal communication. Professor: Today we're going to look at how animals communicate, and specifically, we'll focus on the concept of honest signaling. Now, in many species, signals are used to convey information between individuals. For example, a male bird might sing to attract a mate. But here's the question: how can the female trust that the male's song is an honest indicator of his quality? After all, he could just be bluffing. This is where the idea of costly signaling comes in. The theory suggests that for a signal to be reliable, it must be costly to produce. Think of a peacock's tail. It's heavy, cumbersome, and makes the bird more visible to predators. Only a healthy peacock can afford to grow and carry such a tail. So when a peahen sees a large, ornate tail, she knows the male is genetically fit, because if he were sick or weak, he couldn't produce it. Similarly, in some frog species, males call at a frequency that is energetically expensive. Only the strongest males can sustain these calls. So the cost acts as a filter, ensuring that the signal is honest. This principle applies not only to mating but also to other interactions, like warning calls among prey animals. An animal that gives an alarm call may attract the predator's attention, increasing its own risk. So the call is a reliable signal of danger because it's costly to make. Now, let's consider a potential counterexample...