Wow, the Zero Population bunch is going to have a ball with this aren't they? Kooks to the fore!
Once a civilization is established, every person should marry and have exactly 2 kids; more or fewer kids, we grow or shrink toward different kinds of crisises.
Of couse disease and asexuality cause problems, so in reality fewer people actually marry, but those who do need to have more than 2 kids to compensate for stillborns and childless losers....
My supervisor is one of those. She makes the most inappropriate comments to workers who are expecting.
http://www.vhemt.org/
The Voluntary Human Extinction Movement
VHEMT
"May we live long and die out"
Phasing out the human race by voluntarily ceasing to breed will allow Earth's biosphere to return to good health. Crowded conditions and resource shortages will improve as we become less dense.