托福口语 Task 4

Today we're going to talk about a fascinating concept in animal behavior called 'reciprocal altruism.' This is when animals help others who are not their relatives, with the expectation that the favor will be returned in the future. It's a form of cooperation that seems to defy natural selection, but it can evolve if certain conditions are met. Let me give you two classic examples. First, consider vampire bats. A bat that has successfully fed will often regurgitate blood to feed a hungry companion that failed to find food that night. This is costly to the donor because it loses precious energy, but the favor is remembered. Later, when the donor is hungry, the bat it helped before is more likely to return the favor. This works because bats live in stable social groups and remember individuals. Second, think of cleaner fish, like the cleaner wrasse. These small fish set up 'cleaning stations' where larger fish come to have parasites removed. The cleaner fish gets a meal, and the larger fish gets cleaned. However, the cleaner fish could cheat by taking a bite of the larger fish's mucus or scales, which is a bigger meal. But they usually don't because the larger fish will remember and avoid the cheating cleaner, and the cleaner needs the station for future meals. So, in both cases, the benefit of future cooperation outweighs the short-term gain of cheating.