>Marriage practices in Northwest Europe are unique among societies with intensive agriculture. Critically, married couples were freely chosen non-relatives who set up their households independently of their parents and their extended families; households typically including nonrelatives and were established only afer achieving economic viability. This in turn required greater planning and self-control prior to marriage, and resulted in greater husband-wife partnership than is typical when marriage is embedded within extended kinship networks (i.e., joint family structure—a form of collectivism paradigmatically occurring in the Middle East). A standard view among historians is that this marriage regime was a response to the unique context afer the fall of the Roman Empire in which lords were forced to give incentives to laborers. This hypothesis is rejected for several reasons: 1. there are strong currents of individualism in Indo-European culture long predating the post-Roman period; 2. the manorial system of the post-Roman world was remarkably similar to the prevailing practices of Germanic tribes during the Roman period; 3. individualist families have several disadvantages compared to collectivist families, including later generation time, uncertain inheritance, greater likelihood of sexual assault prior to marriage in households composed of non-relatives—thus making it unlikely to be freely chosen because of incentives provided by lords. This is compatible with a theory that European individualism results from genetically based tendencies resulting in a misft with medieval environments compared to collectivist family structure. Data are reviewed indicating that the most extreme forms of individualism occur in Scandinavian societies, implying a cline in individualism from southeast to northwest. In conclusion, an ethnically based northwest-southeast gradient is proposed as the main variable in explaining variation in family structure within Western Europe. However, viewed in broader terms—in comparison, say, to the Middle East—all of Europe, including Eastern Europe, is relatively individualistic.