Exaptation
The physical features of an animal's body usually serve a specific purpose- they function to increase the animal's chances of survival. But over time in response to a particular challenge in its environment an animal species will sometimes use one of its existing features for a new purpose. This is known as exaptation. By finding another use for one of its physical features exaptation allows animals to respond to additional challenges in their environment. The animal may continue to use the physical feature for its older purpose while also using it for the new purpose.
听力材料：
Now listen to part of a lecture from a biology class.
So, okay, let me tell you about a great example of this. There's a bird, a type of heron that lives near rivers and marshes in Africa. Now this heron is a waiting bird. It spends most of its time walking around in shallow water. And during the day, it eats the fish that swim in the rivers and marshes. The trouble is though it can be pretty hard to see the fish with the sun shining on the water, because the sunlight creates a lot of glare and reflections, making it tough to see fish swimming below the surface.
But over time, this species of heron has found a cool solution involving the use of its wings. Like most birds, the heron uses its wings for flying. But what happened is at some point in the past, the heron also started using its wings to block the sun, to create shade when it's looking for fish. It does this by putting its wings above its head and holding them there. While it looks down into the water, with its back to the sun and its wings above its head. The wings form a kind of canopy or umbrella that blocks the sun and eliminate the glare on the water. So the heron is able to see the fish much better.
Question：
Explain how the example of the heron illustrates exaptation.
