Question:

Until the Industrial Revolution, the peppered moth was mainly white with black spots. As London’s air became thick with soot from factories, the once-white trees the moths used to live on became blacker. Birds were now able to spot and eat the moths that were white on the black trees. However, some moths had more black spots than others, making them harder for the birds to spot than their whiter relatives. These moths survived and passed the genetic trait of being darker to their offspring. This passage describes what theory?