Social complexity and the fractal structure of group size in primate social evolution
Social complexity and the fractal structure of group size in primate social evolution
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DOI：
10.1111/brv.12730
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发表时间：
2021-05-04
影响因子：
10
通讯作者：
Shultz, Susanne
中科院分区：
文献类型：
--
作者：
Dunbar, Robin I. M.;Shultz, Susanne
与大多数其他哺乳动物和鸟类相比，类人灵长类动物的社会异常复杂，其特点是有紧密的社会群体。在灵长类动物中，这种效应被概括在社会大脑假说中：社会复杂性的各种指标（社会群体规模、梳理集团规模、战术行为、联盟形成）与大脑大小之间存在强有力的相关性。迄今为止，这一直被解释为一种简单、单一的关系。使用来自四个独立大脑数据库的五个不同脑体积指数的数据，我们表明，根据大脑大小绘制的群体大小分布最好描述为一组四个不同的、定义非常狭窄的等级，这些等级与系统发育无关。在不同的数据集和大脑指数中，这些等级的属分配是高度一致的。我们表明这些等级对应于有联系的社会群体的逐步演变。此外，我们还表明，对于那些生活在多层次社会系统中的物种，每种情况下不同分组级别的典型大小与不同的等级一致。这表明这些等级对应于特别稳定的人口吸引因素。使用五种不同的认知指数，我们表明成绩与社交认知技能的提高相关，这表明管理群体凝聚力的认知需求在各个年级逐渐增加。我们认为，等级本身代表了动物在觅食过程中维持社会和空间一致性的能力的玻璃天花板，并且为了进化出更紧密联系的群体，物种必须能够投资于昂贵的认知形式。
Compared to most other mammals and birds, anthropoid primates have unusually complex societies characterised by bonded social groups. Among primates, this effect is encapsulated in the social brain hypothesis: the robust correlation between various indices of social complexity (social group size, grooming clique size, tactical behaviour, coalition formation) and brain size. Hitherto, this has always been interpreted as a simple, unitary relationship. Using data for five different indices of brain volume from four independent brain databases, we show that the distribution of group size plotted against brain size is best described as a set of four distinct, very narrowly defined grades which are unrelated to phylogeny. The allocation of genera to these grades is highly consistent across the different data sets and brain indices. We show that these grades correspond to the progressive evolution of bonded social groups. In addition, we show, for those species that live in multilevel social systems, that the typical sizes of the different grouping levels in each case coincide with different grades. This suggests that the grades correspond to demographic attractors that are especially stable. Using five different cognitive indices, we show that the grades correlate with increasing social cognitive skills, suggesting that the cognitive demands of managing group cohesion increase progressively across grades. We argue that the grades themselves represent glass ceilings on animals' capacity to maintain social and spatial coherence during foraging and that, in order to evolve more highly bonded groups, species have to be able to invest in costly forms of cognition.