Department of Anthropology, University of Michigan, 1085 South University Avenue, Ann, Arbor, MI, USA.
Department of Anthropology, University of Michigan, 1085 South University Avenue, Ann, Arbor, MI, USA.
J Hum Evol. 2020 Jul;144:102813. doi: 10.1016/j.jhevol.2020.102813. Epub 2020 May 25.
Primates frequently form affiliative relationships that have important fitness consequences. Affiliative relationships between unrelated males and females are ubiquitous in humans but are not widely reported in humans' closest living relatives, chimpanzees (Pan troglodytes). Instead, adult male chimpanzees are extremely aggressive to females, using the aggression to coerce females to mate with them. Adolescent male chimpanzees are physically and socially immature and unable to use aggression toward females in the same way as adult males. Instead, adolescent males might build affiliative relationships with females as an alternative tactic to increase their chances of mating and reproducing. To investigate this possibility, we recorded social interactions between 20 adolescent and 10 young adult males and 78 adult female chimpanzees over 2 years at Ngogo in Kibale National Park, Uganda. Analyses using grooming and proximity as assays revealed that adolescent and young adult males formed differentiated, affiliative relationships with females. These relationships were as strong as the bonds young males formed with maternal kin and unrelated males and increased in strength and number as males aged and started to dominate females. Male-female relationships extended outside the immediate context of mating. Although males affiliated slightly more often with females when they were cycling, they also did so when females were pregnant and nursing young infants. Males and females who formed bonds reassured each other, looked back and waited for each other while traveling, and groomed more equitably than other male-female pairs, even after the time they spent together in association and the female's reproductive state were taken into account. Despite the affiliative nature of these relationships, adolescent and young adult males selectively targeted their female partners for aggression. These findings provide new insights into the evolution of social bonds between human females and males, which can involve both affiliation and coercive violence.
灵长类动物经常形成具有重要适应意义的亲密关系。在人类中，无亲缘关系的雄性和雌性之间存在广泛的亲密关系，但在人类最亲近的亲属——黑猩猩（Pan troglodytes）中却很少有报道。相反，成年雄性黑猩猩对雌性极具攻击性，利用这种攻击性强迫雌性与它们交配。青春期雄性黑猩猩在身体和社交上都不成熟，无法像成年雄性那样对雌性使用攻击性。相反，青春期雄性可能会与雌性建立亲密关系，作为增加交配和繁殖机会的替代策略。为了研究这种可能性，我们在乌干达基巴莱国家公园的恩戈格记录了 20 只青春期雄性和 10 只青年成年雄性与 78 只成年雌性黑猩猩在 2 年中的社交互动。使用梳理和接近作为检测方法的分析表明，青春期和青年成年雄性与雌性形成了分化的、亲密的关系。这些关系与年轻雄性与母系亲属和无亲缘关系的雄性形成的关系一样紧密，并随着雄性的年龄增长和开始支配雌性而增强和增加。雄性和雌性之间的关系超出了交配的直接背景。尽管雄性在发情期与雌性的互动更频繁，但它们在雌性怀孕和哺乳幼崽时也会这样做。形成纽带的雄性和雌性会相互安慰，在旅行时会回头等待对方，梳理时会比其他雄性和雌性的配对更加平等，即使在考虑到它们在一起的时间和雌性的繁殖状态之后也是如此。尽管这些关系具有亲密的性质，但青春期和青年成年雄性会选择性地将其雌性伴侣作为攻击目标。这些发现为人类男性和女性之间社会关系的进化提供了新的见解，这些关系既可以包括亲密关系，也可以包括强制性暴力。
