Why are populations, rather than individuals, the units of evolution?

Which sentence best expresses the differing opinions of these two book reviews?

What is point source pollution of an aquatic ecosystem? a) pollution of freshwater sources b) pollution from many sources that combine into one c) pollution that occurs over a wide area; water that runs off from fields, parking lots, and other land surfaces d) pollution that can easily be identified with a single discharge source, such as an open pipe which drains into a body of water

At the beginning of the virtual lab, you were asked to sort eight lizards into categories. what criteria did you initially use to make your groups? did you revise your criteria later? why?