Brains, brawn and sociality: a hyaena's tale

Abstract

Theoretically intelligence should evolve to help animals solve specific types of problems posed by the environment, but it remains unclear how environmental complexity or novelty facilitates the evolutionary enhancement of cognitive abilities, or whether domain-general intelligence can evolve in response to domain-specific selection pressures. The social complexity hypothesis, which posits that intelligence evolved to cope with the labile behaviour of conspecific group-mates, has been strongly supported by work on the sociocognitive abilities of primates and other animals. Here we review the remarkable convergence in social complexity between cercopithecine primates and spotted hyaenas, and describe our tests of predictions of the social complexity hypothesis in regard to both cognition and brain size in hyaenas. Behavioural data indicate that there has been remarkable convergence between primates and hyaenas with respect to their abilities in the domain of social cognition. Furthermore, within the family Hyaenidae, our data suggest that social complexity might have contributed to enlargement of the frontal cortex. However, social complexity failed to predict either brain volume or frontal cortex volume in a larger array of mammalian carnivores. To address the question of whether or not social complexity might be able to explain the evolution of domain-general intelligence as well as social cognition in particular, we presented simple puzzle boxes, baited with food and scaled to accommodate body size, to members of 39 carnivore species housed in zoos and found that species with larger brains relative to their body mass were more innovative and more successful at opening the boxes. However, social complexity failed to predict success in solving this problem. Overall our work suggests that, although social complexity enhances social cognition, there are no unambiguous causal links between social complexity and either brain size or performance in problem-solving tasks outside the social domain in mammalian carnivores.

Markedly Elevated Antibody Responses in Wild versus Captive Spotted Hyenas Show that Environmental and Ecological Factors Are Important Modulators of Immunity

“…Pathogen transmission is often positively correlated with host density, and the effect becomes more pronounced in species that live in large aggregations [44]. Wild hyenas live in social groups that can include more than 100 individuals [45]. By contrast, captive hyenas are housed in groups of two or three.…”

Socioecological predictors of immune defences in wild spotted hyenas

“…Hyena societies, or clans, may contain up to 130 individuals, and clans are rigidly structured by linear rank relationships that are stable over time (Frank ; Holekamp et al . ). Within each clan social rank is learned during the first several months of life, with the cubs assuming ranks immediately below those of their mothers, and thus dominance is not determined by size or fighting ability (Kruuk ; Holekamp & Smale ; Smale, Frank & Holekamp ; Smith ).…”

The evolution of intelligence in mammalian carnivores

“…At the neurological level, modules are often conceptualized as dedicated brain areas serving domain-specific cognitive functions or behaviour patterns that can be selectively activated or inhibited; for example the suprachiasmatic nucleus mediates time-keeping in mammals [6], and sleep is mediated by a cluster of ventrolateral preoptic neurons that innervate the tuberomammillary nucleus [7]. Abundant evidence shows that certain species are exceptionally good at solving some types of socio-ecological problems, but not others [8,9], and that these specialized abilities enhance fitness [10,11]. Thus there is a great deal of empirical support for the evolution and maintenance of domain-specific cognitive abilities in both humans [12] and non-human animals.…”