Rachel counted all the earthworms in a square meter in her back yard and found she had 36. She went back a week later and found she had only 30.Rachel knew that this was far too few to maintain her lawn so she decided to study the population for a couple of weeks. She found there were 9 worms born per week and 5 died per week. She also found 10 left for a nearby plot of land and 8 worms came from nearby plots during that week. Was the population growing or shrinking

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.