There are as many men as there are pregnant women standing outside the vault waiting to come back in. When a pregnancy ends, a man comes in and immediately starts a new one. All of the rest of the dwellers spend all their time exploring the wastes. They occasionally come back to briefly partake of the stimpaks and radaways produced by the vault. Low happiness mostly prevents production, but because everyone in the vault is immortal I can rush with impunity. When children grow up, they are sent out into the waste before they can be killed by radroaches.