托福口语 Task 4

Today we're going to talk about a fascinating behavior in the animal kingdom called 'reciprocal altruism.' This is when animals help others not because they expect an immediate reward, but because they may receive help in return at a later time. One classic example comes from vampire bats. These bats need to feed on blood every night, but they sometimes fail to find a meal. When a bat returns to the roost hungry, another bat that has fed successfully will regurgitate some blood to share with the hungry one. Interestingly, the bat that shares is more likely to receive help from the same individual on a future night when it's the one in need. This exchange isn't just random kindness—it's a calculated system of mutual support among roost mates. Another example is seen in certain species of fish, like the cleaner wrasse. These small fish set up 'cleaning stations' where larger fish come to have parasites removed. The cleaner wrasse gets a meal, and the larger fish gets cleaned. But what's remarkable is that when a larger predator arrives, the cleaner wrasse sometimes 'dances' or touches the predator to signal that it's a cleaner, and the predator refrains from eating it. This cooperation benefits both sides, and it's built on trust that the cleaner won't be eaten and the predator won't be harmed. So in both cases, the animals engage in seemingly selfless acts that actually provide long-term benefits to the group and to themselves.