because math All it takes is one tiny subpopulation with more than 2 kids per woman, and you get exponential growth. Exponential growth conquers all. If you ha

because math All it takes is one tiny subpopulation with more than 2 kids per woman, and you get exponential growth. Exponential growth conquers all. If you have a computer science background, think back to big-O notation. Having 4 kids per woman (thus 2 per person) is a growth rate that doubles the population every generation. So, do the Amish exist? Yes they do. That alone ensures that growth will not stop. Even if everybody else decided to not reproduce, we'd be well above the current world population after a few centuries.