Socioecological environments that promote frequent interaction and social tolerance have favored the evolution of strong and equitable social bonds, which facilitate cooperation and confer fitness benefits. In most species, kinship is the primary predictor of bond strength and quality, but it does not adequately explain partner choice among adult male chimpanzees. Instead, most bonds and cooperative interactions occur among unrelated individuals, likely because of a lack of brothers among available partners. To identify what factors drive partner choice when kinship does not, we investigated the strength and quality of social bonds among adult male chimpanzees (N = 26) at Gombe National Park, Tanzania. Maternal brothers, when present, formed stronger bonds than other dyads, and maternal brothers who were close in age or rank formed the strongest bonds. Among dyads that were not maternal brothers, however, the strength of social bonds was not associated with either age difference or rank difference. Additionally, dyads with stronger bonds groomed more equitably than other dyads, as did maternal brothers and dyads close in rank. Bonds were stable, community-wide, for 2 years on average, while lasting up to 13 years. Overall, there remains no clear-cut explanation for partner choice among male chimpanzees. Demographic constraints limit the impact of kinship, and the effects of age and rank difference are small or nonexistent, suggesting that bond strength results from a more complex process than a simple accounting of basic characteristics. Instead, dyads may possess some distinct quality that engenders strength and stability, such as compatible personalities. Strong social ties are associated with increased fitness in several species, including humans, baboons, feral horses, and dolphins. Although close kin typically form the strongest bonds, kinship explains only a limited number of bonds (and associated cooperation) among adult male chimpanzees. To identify what factors influence partner choice when kinship does not, we examined social bonds among adult male chimpanzees at Gombe National Park, Tanzania. Males formed strong, stable bonds and groomed more equitably with strong bond partners. Nevertheless, kinship, age difference, and rank difference did not fully explain male partner choice. These results contrast with findings in other species, where stronger and more equitable bonds are typically formed by kin as well as those that are close in age and rank. Instead, male chimpanzee dyads may possess some distinct quality that promotes strength and stability, such as compatible personalities.

中文翻译：

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成年雄性黑猩猩（Pan troglodytes schweinfurthii）之间的社会关系：社会联系强度和质量的变化

促进频繁互动和社会宽容的社会生态环境有利于强大而公平的社会纽带的发展，这促进了合作并赋予了健康益处。在大多数物种中，亲属关系是纽带强度和质量的主要预测因素，但它并不能充分解释成年雄性黑猩猩的伴侣选择。相反，大多数联系和合作互动发生在无关的个人之间，可能是因为可用合作伙伴之间缺乏兄弟。为了确定当亲属关系不存在时是什么因素驱动伴侣选择，我们调查了坦桑尼亚贡贝国家公园成年雄性黑猩猩（N = 26）之间社会联系的强度和质量。母系兄弟在场时比其他双胞胎形成了更牢固的纽带，与年龄相近或等级相近的兄弟姐妹形成了最牢固的纽带。然而，在不是母兄弟的二人组中，社会纽带的强度与年龄差异或等级差异无关。此外，具有更强纽带的二元组比其他二元组更公平地梳理，母系兄弟和二元组在等级上也很接近。债券在整个社区范围内保持稳定，平均期限为 2 年，最长可达 13 年。总的来说，对于雄性黑猩猩的伴侣选择，仍然没有明确的解释。人口统计学限制限制了亲属关系的影响，年龄和等级差异的影响很小或不存在，这表明结合强度是由一个比基本特征的简单计算更复杂的过程产生的。反而，双子座可能具有一些独特的品质，可以产生力量和稳定性，例如相容的个性。强大的社会联系与几种物种的健康状况的增加有关，包括人类、狒狒、野马和海豚。尽管近亲通常会形成最强的纽带，但亲属关系仅能解释成年雄性黑猩猩之间数量有限的纽带（以及相关的合作）。为了确定当亲属关系不存在时哪些因素会影响伴侣选择，我们检查了坦桑尼亚贡贝国家公园成年雄性黑猩猩之间的社会联系。男性形成了牢固、稳定的纽带，并且与强大的纽带伙伴相处得更公平。然而，亲属关系、年龄差异和等级差异并不能完全解释男性伴侣的选择。这些结果与其他物种的发现形成对比，在这种情况下，亲属以及年龄和等级相近的人通常会形成更牢固、更公平的联系。相反，雄性黑猩猩可能具有一些促进力量和稳定性的独特品质，例如相容的个性。