oh ok! I just figured, if there are male and female dwarves but they can’t tell which is which (and don’t care, socially) you’d end up with about half of all long-term couples being infertile. so I figured, if you’re in a fertile couple and your sibling is in an infertile couple, you’d have like five kids and raise them together with your sibling and their spouse, then maybe when they get older some of them go live with your sibling full-time. so dwarves live in big family groups.