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Barton, R. A. (1996). Neocortex size and behavioural ecology in primates. Proc. R. Soc. Lond. B, 263(1367), 173–177.
Abstract: The neocortex is widely held to have been the focus of mammalian brain evolution, but what selection pressures explain the observed diversity in its size and structure? Among primates, comparative studies suggest that neocortical evolution is related to the cognitive demands of sociality, and here I confirm that neocortex size and social group size are positively correlated once phylogenetic associations and overall brain size are taken into account. This association holds within haplorhine but not strepsirhine primates. In addition, the neocortex is larger in diurnal than in nocturnal primates, and among diurnal haplorhines its size is positively correlated with the degree of frugivory. These ecological correlates reflect the diverse sensory-cognitive functions of the neocortex.
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Joffe, T. H., & Dunbar, R. I. (1997). Visual and socio-cognitive information processing in primate brain evolution. Proc Biol Sci, 264(1386), 1303–1307.
Abstract: Social group size has been shown to correlate with neocortex size in primates. Here we use comparative analyses to show that social group size is independently correlated with the size of non-V1 neocortical areas, but not with other more proximate components of the visual system or with brain systems associated with emotional cueing (e.g. the amygdala). We argue that visual brain components serve as a social information 'input device' for socio-visual stimuli such as facial expressions, bodily gestures and visual status markers, while the non-visual neocortex serves as a 'processing device' whereby these social cues are encoded, interpreted and associated with stored information. However, the second appears to have greater overall importance because the size of the V1 visual area appears to reach an asymptotic size beyond which visual acuity and pattern recognition may not improve significantly. This is especially true of the great ape clade (including humans), that is known to use more sophisticated social cognitive strategies.
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Hoff, M. P., Powell, D. M., Lukas, K. E., & Maple, T. L. (1997). Individual and social behavior of lowland gorillas in outdoor exhibits compared with indoor holding areas. Appl. Anim. Behav. Sci., 54(4), 359–370.
Abstract: The behavior of nine lowland gorillas (Gorilla gorilla gorilla) living in three social groups at Zoo Atlanta was compared in an indoor holding area versus an outdoor exhibit. Focal animal data were collected for each animal during 15 min observation sessions, alternating between indoors and outdoors. A variety of solitary and social behaviors differed in the two conditions. All individual and social behaviors that showed a difference, except eating, occurred more indoors than outdoors. These included aggressive displays, reclining, self manipulation, and social examination of others. Additionally, the gorillas spent more time closer together in the indoor condition. A variety of other behaviors measured did not change between the two environments. There was a clear effect on behavior of the different housing conditions in which the gorillas were kept. It is suggested that the differences in aggressive behavior may be related to environmental complexity. It is further suggested that zoos should be aware that differences in behavior reported by caretaking staff, researchers and visitors may be a reflection of the differing environmental circumstances in which the animals are observed.
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Gallup, G. G. J. (1997). On the rise and fall of self-conception in primates. Ann N Y Acad Sci, 818, 72–82.
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Swartz, K. B. (1997). What is mirror self-recognition in nonhuman primates, and what is it not? Ann N Y Acad Sci, 818, 64–71.
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Sterck, E., Watts, D., & van Schaik, C. (1997). The evolution of female social relationships in nonhuman primates. Behav. Ecol. Sociobiol., 41(5), 291–309.
Abstract: Considerable interspeci®c variation in female social relationships occurs in gregarious primates, particularly with regard to agonism and cooperation between females and to the quality of female relationships with males. This variation exists alongside variation in female philopatry and dispersal. Socioecological theories have tried to explain variation in female-female social relationships from an evolutionary perspective focused on ecological factors, notably predation and food distribution. According to the current ``ecological model'', predation risk forces females of most diurnal primate species to live in groups; the strength of the contest component of competition for resources within and between groups then largely determines social relationships between females. Social elationships among gregarious females are here characterized as DispersalEgalitarian, Resident-Nepotistic, Resident-Nepotistic-Tolerant, or Resident-Egalitarian. This ecological model has successfully explained i€erences in the occurrence of formal submission signals, decided dominance relation ships, coalitions and female philopatry. Group size and female rank generally a€ect female reproduction success as the model predicts, and studies of closely related species in di€erent ecological circumstances underscore the importance of the model. Some cases, however, can only be explained when we extend the model to incorporate the e€ects of infanticide risk and habitat saturation. We review evidence in support of the ecological model and test the power of alternative models that invoke between-group competition, forced female philopatry, demographic female recruitment, male interventions into female aggression, and male harassment.
Not one of these models can replace the ecological model, which already encompasses the between-group competition. Currently the best model, which explains
several phenomena that the ecological model does not, is a ``socioecological model'' based on the combined importance of ecological factors, habitat saturation and infanticide avoidance. We note some points of similarity and divergence with other mammalian taxa; these remain to be explored in detail.
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Kendrick, K. M. (1998). Intelligent perception. Appl. Anim. Behav. Sci., 57(3-4), 213–231.
Abstract: For an animal from any species to exhibit intelligent perception it must be capable of being consciously aware of what it perceives and capable of learning from this experience. Although many organisms, and for that matter machines, are capable of rapid adaptive learning in response to perception of environmental changes, such adaptations can occur without them being consciously aware either of external stimuli or their response to them. While behavioural and neurophysiological evidence suggests that, apart from ourselves, other higher primates must also be capable of such awareness, an important central question is whether such awareness is a characteristic of primate evolution or if it also occurs in sub-primate mammals as well. In this review I will examine our behavioural and neurophysiological evidence from visual and olfactory recognition studies in the sheep to support the argument that they are likely to be aware of and learn about both social and non-social objects and that they are therefore capable of intelligent perception. However, the impact of motivational changes on these perceptual processes suggests that they may be limited in terms of both prospection and retrospection and dealing with symbolic associations.
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Dunbar, R. I. M. (1998). The social brain hypothesis. Evol. Anthropol., 6(5), 178–190.
Abstract: Conventional wisdom over the past 160 years in the cognitive and neurosciences has assumed that brains evolved to process factual information about the world. Most attention has therefore been focused on such features as pattern recognition, color vision, and speech perception. By extension, it was assumed that brains evolved to deal with essentially ecological problem-solving tasks. © 1998 Wiley-Liss, Inc.
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Pennisi, E. (1999). Are out primate cousins 'conscious'? (Vol. 284).
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de Waal, F. B., Aureli, F., & Judge, P. G. (2000). Coping with crowding. Sci Am, 282(5), 76–81.
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