Roberts Sam G B, Roberts Anna I
Department of Psychology, University of Chester Chester, UK.
Front Psychol. 2016 Nov 24;7:1756. doi: 10.3389/fpsyg.2016.01756. eCollection 2016.
A key driver of brain evolution in primates and humans is the cognitive demands arising from managing social relationships. In primates, grooming plays a key role in maintaining these relationships, but the time that can be devoted to grooming is inherently limited. Communication may act as an additional, more time-efficient bonding mechanism to grooming, but how patterns of communication are related to patterns of sociality is still poorly understood. We used social network analysis to examine the associations between close proximity (duration of time spent within 10 m per hour spent in the same party), grooming, vocal communication, and gestural communication (duration of time and frequency of behavior per hour spent within 10 m) in wild chimpanzees. This study examined hypotheses formulated a priori and the results were not corrected for multiple testing. Chimpanzees had differentiated social relationships, with focal chimpanzees maintaining some level of proximity to almost all group members, but directing gestures at and grooming with a smaller number of preferred social partners. Pairs of chimpanzees that had high levels of close proximity had higher rates of grooming. Importantly, higher rates of gestural communication were also positively associated with levels of proximity, and specifically gestures associated with affiliation (greeting, gesture to mutually groom) were related to proximity. Synchronized low-intensity pant-hoots were also positively related to proximity in pairs of chimpanzees. Further, there were differences in the size of individual chimpanzees' proximity networks-the number of social relationships they maintained with others. Focal chimpanzees with larger proximity networks had a higher rate of both synchronized low- intensity pant-hoots and synchronized high-intensity pant-hoots. These results suggest that in addition to grooming, both gestures and synchronized vocalizations may play key roles in allowing chimpanzees to manage a large and differentiated set of social relationships. Gestures may be important in reducing the aggression arising from being in close proximity to others, allowing for proximity to be maintained for longer and facilitating grooming. Vocalizations may allow chimpanzees to communicate with a larger number of recipients than gestures and the synchronized nature of the pant-hoot calls may facilitate social bonding of more numerous social relationships. As group sizes increased through human evolution, both gestures and synchronized vocalizations may have played important roles in bonding social relationships in a more time-efficient manner than grooming.
灵长类动物和人类大脑进化的一个关键驱动因素是管理社会关系所产生的认知需求。在灵长类动物中，梳理毛发在维持这些关系方面起着关键作用，但用于梳理毛发的时间本质上是有限的。交流可能作为一种额外的、更节省时间的与梳理毛发互补的建立联系机制，然而交流模式与社交模式之间的关系仍未得到很好的理解。我们运用社会网络分析来研究野生黑猩猩中近距离接触（每小时在同一群体中处于10米范围内的时长）、梳理毛发、声音交流以及手势交流（每小时在10米范围内行为的时长和频率）之间的关联。本研究检验了预先设定的假设，且结果未针对多重检验进行校正。黑猩猩有着不同的社会关系，焦点黑猩猩与几乎所有群体成员都保持着一定程度的近距离接触，但会向较少数量的偏好社交伙伴做出手势并为其梳理毛发。近距离接触程度高的黑猩猩对之间的梳理毛发频率更高。重要的是，更高频率的手势交流也与近距离接触程度呈正相关，特别是与亲和相关的手势（问候、互相梳理的手势）与近距离接触有关。同步的低强度呼呼叫声在黑猩猩对之间也与近距离接触呈正相关。此外，个体黑猩猩近距离接触网络的规模存在差异——即它们与其他个体维持的社会关系数量。近距离接触网络规模较大的焦点黑猩猩同步低强度呼呼叫声和同步高强度呼呼叫声的频率都更高。这些结果表明，除了梳理毛发外，手势和同步发声可能在让黑猩猩管理庞大且不同的社会关系集方面都发挥着关键作用。手势在减少因与他人近距离接触而产生的攻击性方面可能很重要，从而使近距离接触能维持更长时间并促进梳理毛发。发声可能使黑猩猩能够与比手势更多的接收者进行交流，并且呼呼叫声的同步性质可能有助于更多社会关系的社会联结。随着人类进化过程中群体规模的增加，手势和同步发声可能在以比梳理毛发更节省时间的方式建立社会关系方面都发挥了重要作用。
