Unveiling animal death cognition: the role of social systems.

As studies aimed at clarifying the evolution of cognition in animals accumulate, some non-human primates are widely considered to be the most cognitively advanced species after humans. Cognitive processes related to social interaction and emotional responsiveness may also play a role in primates' responses to death and dying; however, how social complexity might influence animals' understanding of death remains under-explored. Here, we connect evolutionary development and social systems to death cognition, and establish a five-dimensional framework for comparative purposes, based on existing thanatological studies. Of 135 species included in the analysis, dolphins, elephants and chimpanzees-species with highly complex societies-were shown to have a more advanced death understanding than other taxonomically close species. Focusing on a multilevel society primate, the golden snub-nosed monkey (Rhinopithecus roxellana), we present five death-related case studies involving behavioral, physiological, and social responses to dead conspecifics. Despite evolving on an older phylogenetic branch than that leading to modern hominids, these monkeys display prolonged dead-infant carrying, care/caretaking, silence and compassion, and revisitation of corpses at levels comparable to those seen in chimpanzees, more than other, non-multilevel society primates. In addition to introducing a novel approach to the comparative and evolutionary study of death-related behavior, we suggest that social complexity can exert a modulatory influence on phylogenetic factors that constrain the baseline cognitive architecture, allowing more nuanced expressions of death cognition.