They must learn that an object still exists even though they can’t see it.
Answer:
any external change in their environment that causes one phenotype to have an advantage over the other
Explanation:
There are a few possible answers here. A good example might be if the grass they live in turns brown after a long drought, leaving the green grasshoppers more visible to predators than brown ones.
Answer:
There are over thirty principal meridians in the US.
Explanation: