Department of Psychology, University of Michigan, Ann Arbor, MI, USA.
Proc Biol Sci. 2010 Oct 7;277(1696):3045-53. doi: 10.1098/rspb.2010.0580. Epub 2010 May 12.
Although monitoring social information is a key aspect of the social complexity hypothesis, surprisingly little work has compared social knowledge across different species of wild animals. In the present study, I use playback experiments to test for individual recognition in wild male geladas (Theropithecus gelada) to compare with published accounts of social knowledge in chacma baboons (Papio ursinus). Geladas and baboons are closely related primates living in socially complex groups that differ dramatically in group size-geladas routinely associate with more than 10 times the number of conspecifics than do baboons. Using grunts from non-rival males to simulate approaches, I examined the strength of a subject male's response when the 'approach' was from the direction of (i) non-rival males (control), or (ii) rival males (a more salient stimulus if playback grunts are not recognized by the subject). I compared responses separately based on the degree of social overlap between the caller and the subject. Responses indicate that male geladas, unlike baboons, do not use vocalizations to recognize all of the individuals they regularly encounter. This represents, to my knowledge, the first documented evidence of 'missing' social knowledge in a natural primate population. The sharp distinction between baboons and geladas suggests that geladas are either unable or unmotivated to keep track of the individual identity of other males in their multi-level society-even males with whom they have a large degree of social overlap. Thus, these results are consistent with the central assumption of the social complexity hypothesis that social cognition is costly.
尽管监测社会信息是社会复杂性假说的一个关键方面，但令人惊讶的是，很少有研究比较过不同野生动物物种的社会知识。在本研究中，我使用回放实验来测试野生雄性狒狒（Theropithecus gelada）的个体识别能力，以与已发表的狒狒（Papio ursinus）社会知识进行比较。狒狒和山魈是密切相关的灵长类动物，生活在社会结构复杂的群体中，群体规模差异巨大——山魈通常与同物种的个体数比狒狒多 10 倍以上。我使用非竞争雄性的呼噜声来模拟接近，当“接近”来自（i）非竞争雄性（对照）或（ii）竞争雄性（如果播放的呼噜声不被目标雄性识别，这是一个更明显的刺激）时，我检查了目标雄性的反应强度。我根据呼叫者和目标雄性之间的社会重叠程度分别比较了反应。研究结果表明，雄性山魈不像狒狒那样，不使用叫声来识别它们经常遇到的所有个体。这代表了，据我所知，在一个自然灵长类群体中首次记录到“缺失”社会知识的证据。狒狒和山魈之间的鲜明区别表明，山魈要么无法，要么没有动力去跟踪它们多层次社会中其他雄性的个体身份——即使是与它们有很大社会重叠的雄性。因此，这些结果与社会复杂性假说的核心假设一致，即社会认知是有代价的。
