Countries around the world differ dramatically in how long their populations live on average. As you can see in Figure 4.2, the current range extends

Longevity, Health, and Functioning 113

Figure 4.2 International data on average life expectancy at birth. Note the differences between developed and developing countries.

Source: http://www. census. gov/ipc/www/idb/tables. html.

from 38 years in Sierra Leone in Africa to 80 years in Japan. Such a wide divergence in life expectancy reflects vast discrepancies in genetic, sociocultural

and economic conditions, health care, disease, and the like across industrialized and developing nations.

Concept Checks

1. What are some of the main reasons that average longevity increased during the 20th century?

2. What evidence is there that genetics influences average longevity? What are the key environmental influences on average longevity?

3. What are some of the reasons for ethnic differences in average longevity?

4. What explanations have been offered to account for women’s longer average longevity?