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 without expecting an immediate reward, but with the understanding that the favor will be returned in the future. This behavior is more common in species with long-term social bonds. Let me give you two examples. First, consider vampire bats. In a colony, a bat that has successfully fed will sometimes regurgitate blood to share with a hungry neighbor who didn't find food. This bat might go hungry that night, but later, when it's the one who fails to feed, that same neighbor—or another bat it has helped—will return the favor. This ensures the colony's survival. Second, think of cleaner fish. These small fish remove parasites from larger fish. They could just eat the parasites and leave, but they often 'dance' to signal their presence, and larger fish don't eat them. The cleaner fish get a meal, and the larger fish get cleaned. Interestingly, if a cleaner fish is observed cheating by biting the client, other fish avoid it. So, the system relies on reputation and reciprocity.