Charles C. Mann in The Atlantic:
In 1970, when I was in high school, about one out of every four people was hungry—“undernourished,” to use the term preferred today by the United Nations. Today the proportion has fallen to roughly one out of 10. In those four-plus decades, the global average life span has, astoundingly, risen by more than 11 years; most of the increase occurred in poor places. Hundreds of millions of people in Asia, Latin America, and Africa have lifted themselves from destitution into something like the middle class. This enrichment has not occurred evenly or equitably: Millions upon millions are not prosperous. Still, nothing like this surge of well-being has ever happened before. No one knows whether the rise can continue, or whether our current affluence can be sustained.
Today the world has about 7.6 billion inhabitants. Most demographers believe that by about 2050, that number will reach 10 billion or a bit less. Around this time, our population will probably begin to level off. As a species, we will be at about “replacement level”: On average, each couple will have just enough children to replace themselves. All the while, economists say, the world’s development should continue, however unevenly. The implication is that when my daughter is my age, a sizable percentage of the world’s 10 billion people will be middle-class.