Overpopulation

I've been reading a lot on world population recently. Currently the world's population is slightly below 7 billion people.

But what's most shocking is that it took approximately 12,000 YEARS for the earth's population to reach 3.3 billion, and only 45 YEARS to DOUBLED.

An additional 3.3 BILLION people have arrived on this planet since 1965, roughly my lifetime. This statistic amazes me.

Why all these people? Where did they come from? I guess I know where they came from, but still.