Why Only Humans Shed Emotional Tears: Evolutionary and Cultural Perspectives

Why Only Humans Shed Emotional Tears: Evolutionary and Cultural Perspectives. Asmir Gračanin, Lauren M. Bylsma, Ad J. J. M. Vingerhoets. Human Nature, https://link.springer.com/article/10.1007/s12110-018-9312-8

Abstract: Producing emotional tears is a universal and uniquely human behavior. Until recently, tears have received little serious attention from scientists. Here, we summarize recent theoretical developments and research findings. The evolutionary approach offers a solid ground for the analysis of the functions of tears. This is especially the case for infant crying, which we address in the first part of this contribution. We further elaborate on the antecedents and (intra- and interpersonal) functions of emotional tears in adults. The main hypothesis that emerges from this overview is that crying evolved as an emotional expression that signals distress and promotes prosocial behaviors in conspecifics. Further, shedding tears may influence the mood of the crier and his/her outlook on life primarily as a consequence of fulfillment of the proposed signaling function of tears. We also describe how cultural phenomena such as ritual weeping nicely fit within this framework, as they often aim to support a request for help to a powerful person or deity and promote social bonding.

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Although there seems to be a consensus among contemporary scientists that weeping is uniquely human, there have been ample anecdotal descriptions of weeping animals (cf. Masson and McCarthy 1995; Vingerhoets 2013). For example, Homer described how a horse expressed its loyalty to its master, Patroclus, by weeping over his death. Also, crocodiles reportedly shed tears, initially not the proverbial (and hypocritical) crocodile tears, but rather to express real suffering when being physically abused
(Vingerhoets 2013). Deer also were said to weep after having shed their horns (Treacher-Collins 1932). Even Darwin (1872) discussed some observations of weeping animals, including macaques and, in particular, elephants. According to Reynolds (1924), weeping is a typical reaction of certain animals (particularly wolves) that signals exhaustion, which results in the tearful animal being placed at the rear of the pack to allow it to rest and recover. Further, Fossey (2000) described how Coco, a gorilla, wept when he was ill. Finally, in the documentary film The Weeping Camel (Davaa and Falorni 2003), the camel mother starts to produce tears at the moment that she reconnects with her previously rejected offspring and allows it to nurse.

However, the only more systematic study on this topic, a survey among people who work with animals professionally, including veterinarians and zookeepers failed to yield even a single observation of a weeping animal (Frey 1985). Murube (2009a) also concludes that animals generally do not produce emotional tears, although he admitted that several anecdotal reports deserve serious attention by investigators. Consequently, we must conclude that we currently do not have sufficient evidence to document weeping in nonhuman animals. If it does occur, it is extremely exceptional. The apparent uniqueness of human weeping suggests that tears might represent a functional response to adaptive challenges specific to the hominid lineage, which is crucial for understanding both the evolved functions and the proximate mechanisms of this complex behavior.