We study norms regulating socially acceptable female behavior and the effects of between-group competition in the mating market on their development. We focus on a case study featuring an inflow of ethnic Greek refugees arriving from Turkey following the Greco-Turkish conflict in the early 20th century and examine how the composition of the incoming refugee population influenced gender norms in the affected localities. We leverage the fact that the conflict in Turkey resulted in a large number of men being captured or executed before they could emigrate. Consequently, women were overrepresented in the refugee population, triggering a competition shock in the mating market. At the time, prevailing norms stigmatized women living outside male-headed households, making female refugees particularly vulnerable to stereotypes of low moral standards. We conjecture that for a sufficient level of competition, a local individual has an incentive to double down on conservative gender norms as a means of undermining the newcomer-competitors, even if this does not align with their true preferences. Individuals invested in the mating prospects of local women may benefit from emphasizing female `purity' as a valued trait, thereby amplifying the locals' comparative advantage over the morally stigmatized competition. We hypothesize that this, in turn, led to an increased value placed on conservative values signaled by female behavior. To study this idea, we exploit the variation in the gender composition of refugees in a given locality as a proxy for the intensity of competition, relying on the as-good-as-random allocation of refugees determined by Greek authorities.