Abstract
Modern humans live in an “exploded” network with unusually large circles of trust that form due to prosociality toward unfamiliar people (i.e. xenophilia). In a set of experiments we demonstrate that semi-free ranging bonobos (Pan paniscus) – both juveniles and young adults – also show spontaneous responses consistent with xenophilia. Bonobos voluntarily aided an unfamiliar, non-group member in obtaining food even when he/she did not make overt requests for help. Bonobos also showed evidence for involuntary, contagious yawning in response to videos of yawning conspecifics who were complete strangers. These experiments reveal that xenophilia in bonobos can be unselfish, proactive and automatic. They support the first impression hypothesis that suggests xenophilia can evolve through individual selection in social species whenever the benefits of building new bonds outweigh the costs. Xenophilia likely evolved in bonobos as the risk of intergroup aggression dissipated and the benefits of bonding between immigrating members increased. Our findings also mean the human potential for xenophilia is either evolutionarily shared or convergent with bonobos and not unique to our species as previously proposed.
Highlights
Modern humans live in an “exploded” network with unusually large circles of trust that form due to prosociality toward unfamiliar people
One hypothesis proposes that human xenophilia was derived in our lineage, which is supported by the larger pattern of xenophobia in most primates – including chimpanzees[8,33,34,35,36]
The aid that bonobos explicitly provided the unfamiliar recipient in obtaining food is consistent with common definitions of proactive prosociality[69,74], while contagious yawning suggests their xenophilia is not completely under voluntary control and is present even when there is zero familiarity
Summary
Modern humans live in an “exploded” network with unusually large circles of trust that form due to prosociality toward unfamiliar people (i.e. xenophilia). These experiments reveal that xenophilia in bonobos can be unselfish, proactive and automatic They support the first impression hypothesis that suggests xenophilia can evolve through individual selection in social species whenever the benefits of building new bonds outweigh the costs. Contemporary hunter-gatherers commonly engage in cooperative interactions among unfamiliar individuals, so did early Homo sapiens (e.g. flexible dispersal, high social fluidity, intergroup alliance and long-distance trade[3,4,5,6,7,8,9]) This extensive circle of trust provides enormous benefits by creating an interconnected and ever-growing market for information, goods and support[10,11,12,13,14,15,16,17,18]. Strangers will become attractive social partners since social networks can be www.nature.com/scientificreports/
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