A species of lizard can range in color from very light brown to very dark brown. It lives in a forest hiding among the dead leaves. One year, a fungus starts to grow over the dead leaves, creating a very powdery white coating. The light colored lizards can now blend in much better with the leaves than the dark lizards.
What are the extreme traits?
What is the middle trait?
What trait(s) are being selected for?
What trait(s) are being selected against?