Interactions with conspecific outsiders as drivers of cognitive evolution

Abstract

The social intelligence hypothesis (SIH) posits that within-group interactions drive cognitive evolution, but it has received equivocal support. We argue the SIH overlooks a major component of social life: interactions with conspecific outsiders. Competition for vital resources means conspecific outsiders present myriad threats and opportunities in all animal taxa across the social spectrum (from individuals to groups). We detail cognitive challenges generated by conspecific outsiders, arguing these select for 'Napoleonic' intelligence; explain potential influences on the SIH; and highlight important considerations when empirically testing these ideas. Including interactions with conspecific outsiders may substantially improve our understanding of cognitive evolution.

Fig. 1. Two aspects of the social intelligence hypothesis (SIH).

Within-group social intelligence is the capacity to succeed in within-group interactions (a); it represents the well-established basis of the SIH as currently framed^, . We argue that the capacity to succeed in interactions with conspecific outsiders should be included in the SIH for a more complete representation of the social environment. Significant cognitive challenges with respect to outsider threats and opportunities include those arising from b conflict with rivals over resources and territory space, c conflict with rivals over breeding or mating opportunities, d contest dynamics when there are adversarial interactions between rivals and e the evaluation of secondary cues (e.g., faecal deposits) containing information about conspecifics. NB: here we use the dwarf mongoose (Helogale parvula), a cooperatively breeding species, to illustrate some of the cognitive challenges posed by outsiders. However, such challenges and resulting Napoleonic intelligence are relevant across the social spectrum (including solitary and pair-bonded species, and those living in a variety of group structures). Dwarf mongoose illustrations: Martin Aveling. Landscape: David Clode.

Fig. 2. Potential effects of conspecific outsider threat on cognition.

a The classic social intelligence hypothesis focuses only on one axis of sociality (within-group interactions, often using group size as a proxy) in driving cognitive evolution; variation in conspecific outsider threats is ignored. Combining within-group and outsider interactions could produce b an additive or c a synergistic effect on cognitive evolution.

Fig. 3. A plurality of metrics is required to measure interactions with conspecific outsiders at different scales.

a ‘Context’ refers to the social landscape in which conspecific outsider interactions occur. In solitary western fence lizards (Sceloporus occidentalis), e.g., long-term observations reveal considerable home-range and territorial overlap. Lizard photograph: D. A. Hofmann. b ‘Frequency’ refers to the rate of relevant interactions with conspecific outsiders. Many socially monogamous birds have high levels of extra-pair mating; for instance, in pair-bonded yellow-breasted chats (Icteria virens), telemetry reveals nocturnal visits to other territories for likely mating opportunities. Yellow-breasted chat photograph: E. Willoughby. c ‘Contests’ refers to the characteristics of actual interactions between conspecific rivals. In chimpanzees (Pan troglodytes), e.g., violent between-group contests can have dramatic consequences for social evolution. Chimpanzee photograph: L. Samuni.