(I) Life expectancy depends on many things, including diet and access to health care. (II) Overall, however, it reflects the conditions under which life is lived. (III) In some countries life is so difficult that the average person cannot hope to live out five decades. (IV) With a few exceptions, most of the world's countries have lost large percentages of their natural ecosystems to development and agriculture. (V) Many of these countries are in Africa, due to the terrible poverty, famine and civil war that afflict that continent.