I just read this statistic yesterday, and it strikes me as apropos of this conversation:

It took until 1830 for the world's human population to reach 1 billion.

It took another 100 years for the population to reach 2 billion.

It then took only 70 years to get to 6 billion.

At this rate, according to some U.N. population projections, the world's human population will be 128 billion by the year 2155.

Considering the rate at which the global population is growing gives some corrolary perspective to mav's language demographic citations. And definitely food for thought...