Nature, Published online: 15 January 2025; doi:10.1038/d41586-024-04150-2An interdisciplinary analysis of ancient DNA obtained from 722 individuals who lived in the region during the Avar period (between about ad 650 and ad 800) shows that two neighbouring communities had strikingly different genetic ancestries. Two family trees comprising six generations and some 500 related individuals reveal that different marriage networks kept these communities genetically distinct despite their shared culture.