The variation may already exist within the population, but often the variation comes from a mutation, or a random change in an organism's genes.
Answer:
Kettlewell thought that if natural selection caused the change in the moth population, the following must be true: Heavily polluted forests will have mostly dark peppered moths. Clean forests will have mostly light peppered moths. Dark moths resting on light trees are more likely than light moths to be eaten by birds.
Answer:

A society is choosing to replace its nuclear power plants with more sustainable geothermal power plants. Which of the following is an advantage to switching to geothermal power?
A. It can contaminate groundwater.
B. It uses a renewable resource.
C. It consumes a radioactive material.
D. It produces more hazardous waste.
Explanation:

Answer:
D: A density-independent factor.
Explanation:
An earthquake is a density-independent limiting factor
José probably doesn't feel any pain because his body, during and after exercise released endorphins which are endogenous opioids. This endorphins promote a sense of satisfaction and pleasure, and make pain and discomfort feel irrelevant.