托福口语 Task 4

Today, we're going to discuss a fascinating concept in evolutionary biology called 'adaptive radiation.' This occurs when a single ancestral species rapidly diversifies into many new forms to exploit different environments or resources. The key is that this happens over a relatively short period, geologically speaking, and often after a mass extinction or when a species reaches a new, isolated habitat with few competitors. Let me give you two classic examples. First, consider the Hawaiian honeycreepers. A single finch-like ancestor arrived on the islands millions of years ago. Over time, it evolved into over 50 distinct species, each with a different beak shape adapted to a specific food source—some have curved beaks for nectar, others have thick beaks for seeds, and still others have thin, probing beaks for insects. Second, think of the African cichlid fish in Lake Victoria. A few ancestral species colonized the lake, and within a relatively short period, they radiated into hundreds of species, each specializing in different food sources like algae, insects, or other fish, and developing unique jaw structures to match their diets. These examples illustrate how adaptive radiation leads to remarkable biodiversity in isolated ecosystems.