The world's population reached 1 billion in 1804 and only took 123 years to reach 2 billion!

It took the human race until 1804 to reach 1 billion people. Once it reached the first billion though, the population exploded.

Thanks to the Industrial Revolution, better health care and increased access to education, humanity reached it's second billion just 123 years after the first in 1927.

And the population just kept increasing. It reached 3 billion in 1959, 4 billion in 1974, 5 billion in 1987, 6 billion in 1999 and 7 billion in 2011. Crazy!

Experts say that the average life expectancy has increased from 48 years in the 1950s to 68 years today. And while children are much less likely to die while still in infancy, the fertility rate of women has decreased from 6 to 2.5 children.