All of the following may begin an ice age except a. volcanic eruptions b. earths revolution around the sun c. clustering of continents near the poles d. an increased amount of dust particles in earths atmosphere

Which of the following statements is true about the relationship between genetic variation and natural selection? a. genetic variation must be present in a population before natural selection can act on it. b. genetic variation arises in a population as a result of natural selection. c. natural selection can act on a population whether there is genetic variation within the population or not. d. after natural selection acts on a population, the amount of genetic variation in the population always increases.