If Two Have Four in Malvina Reynolds

If two have four and if four have four,
We'll soon be crowded from shore to shore,
But if two have one and some have none,
There'll be room enough for everyone.
Here's a pill, here's a ring,
There are ways of managing everything,
For the sake of the kids who will take our place,
We've got to cut back on the teeming human race.