Another interesting idea for population control is giving every person the right to 3/4 of a child. A couple then has the right to 1.5 children, so they can hav

Another interesting idea for population control is giving every person the right to 3/4 of a child. A couple then has the right to 1.5 children, so they can have one child and sell the right to the remaining half, or they can buy the half they need to get two from another couple. Or even sell/buy 1.5. (This idea is from Kim Stanley Robinson's "Green Mars")