A period of very low rainfall occurred while the Grants were on the islands. The drought resulted in fewer seeds for the finches to eat. Birds with smaller beaks could eat only the smaller seeds. Birds with bigger beaks were better off. They could eat seeds of all sizes. Therefore, there was more food available to them. Many of the small-beaked birds died in the drought. More of the big-beaked birds survived and reproduced. Within just a couple of years, the average beak size in the finches increased. This was clearly evolution by natural selection.
Mark enjoyed walking in the fields and woods near his house. He had walked in the same area as a child and remembered seeing lots of white and brown moths. Now though he did not often see moths. One day while walking he realized that there were several brown moths on a tree after that he noticed them more often he realized that they were just harder to see against the brown trees.
Which moth was easier to see?