My recollection from the book was that, as the sibling comment states, the moon was previously 2:1 men-to-women. It was no longer so by the time of the novel's

My recollection from the book was that, as the sibling comment states, the moon was previously 2:1 men-to-women. It was no longer so by the time of the novel's start, but social norms established during that tumultuous backstory had persisted: mostly the men enforcing good behavior on each other because it was so ridiculously easy to die on the moon and the men were essentially interchangeable to the women and not scarce.