An example of an adaptation that gives an organism greater access to energy

A vestigial structure is a feature of an organism's body that was once an adaptation shaped by natural selection, but which is no longer useful in their current environment. For example, some species of fish that live in completely dark caves have eyes, although their eyes cannot see and serve no function.

I'm into politics, why am i getting these questions? it's 4: 30 am in texas. my paper is due in 2 days. i'm the one needing in political science