Microorganisms cannot experience pain or have other feelings. People ignore environmental problems unless they believe the problems will affect creatures with which they sympathize. The most important environmental problems involve endangered species other than large mammals. An organism can be environmentally significant only if it affects large ecosystems or agriculture.
Publicity campaigns for endangered species are unlikely to have much impact on the most important environmental problems, for while the ease of attributing feelings to large mammals facilitates evoking sympathy for them, it is more difficult to elicit sympathy for other kinds of organisms, such as the soil microorganisms on which large ecosystems and agriculture depend.
Which one of the following is an assumption on which the argument depends?