Question: approximately how long did it take for the human population to reach 1 billion?
Answer: First, the figures. It took all of human history up to 1804 for the world's population to reach 1 billion. But the next billion came only 100 years later, in 1927. And after that, the rate of growth accelerated, 3 billion in 1959, 4 billion 1974, 5 billion 1987, 6 billion 1999, and now 7 billion.