It doesn't have anything to do with evolution itself, but it does have to do with the age of the universe and the earth.
The speed of light in a vacuum is a constant. This constant is known as c. c = 299,792,458 meters per second. Things can certainly affect light, gravity for example, light passing through a medium is likewise different if only fractionally. But passing through a vacuum light always remains c. This means that we can be rather confident that if you, an earthbound observer, peer through a telescope and see stars shining in our next door galactic neighbor, Andromeda, you are seeing light that left that galaxy 2.5 million years ago. Because the light that came from those stars has had to travel the entire distance from its origin to your eyes, and while the journey to your eyes may have been a bumpy one, cosmically speaking, it could not arrive any faster than 2.5 million years.
