Again, discuss the impact on society. Point out that more than 13 million adults were infected with HIV in 1994. By the year 2000, WHO estimates that the total cumulative infection with HIV could reach 30 to 40 million, with 10 million people actually developing AIDS by that point. Encourage students to look up animals in the almanac, encyclopedia, or other references. For each hypothesis, students must explain and cite examples.
Many factors contribute to life expectancy.
Students should look for patterns and generalities, not absolutes, and should control variables. For example, they should compare mammals who live in a similar climate and have similar lifestyles. Much of what we know about the life span of animals comes from zoo records, which are incomplete and often unreliable. Plus, zoo animals tend to live much longer than their wild counterparts.