Objectives Close romantic and friendship relationships are crucial for successful survival and reproduction. Both provide emotional support that can have significant effects on an individual’s health and wellbeing, and through this their longer term survival and fitness. Nonetheless, the factors that create and maintain intimacy in close relationships remain unclear. Nor is it entirely clear what differentiates romantic relationships from friendships in these terms. In this paper, we explore which factors most strongly predict intimacy in these two kinds of relationship, and how these differ between the two sexes. Results Aside from best friendships being highly gendered in both sexes, the dynamics of these two types of relationships differ between the sexes. The intimacy of female relationships was influenced by similarity (homophily) in many more factors (notably dependability, kindness, mutual support, sense of humour) than was the case for men. Some factors had opposite effects in the two sexes: gift-giving had a negative effect on women’s friendships and a positive effect on men’s, whereas shared histories had the opposite effect. Conclusion These results confirm and extend previous findings that the dynamics of male and female relationships are very different in ways that may reflect differences in their functions.

目标 亲密的浪漫关系和友谊关系对于成功的生存和繁殖至关重要。两者都提供情感支持，这可能会对个人的健康和福祉以及由此带来的长期生存和健康产生重大影响。但是，尚不清楚在亲密关系中建立和维持亲密关系的因素。在这些方面，还不清楚什么将浪漫关系与友谊区分开来。在本文中，我们探讨了哪些因素最能预测这两种关系中的亲密关系，以及这两种性别之间的差异。结果 除了最好的友谊在两性之间具有高度性别差异之外，这两种类型的关系的动态在男女之间也有所不同。与男性相比，女性关系的亲密性在许多因素（尤其是可靠性，友善，相互支持，幽默感）中受相似性（同质性）的影响。某些因素对两性有相反的影响：送礼对女性的友谊有负面影响，而对男性则有积极影响，而共享的历史则有相反的影响。结论 这些结果证实并扩展了先前的发现，即男女关系的动态差异很大，可能反映了其功能上的差异。