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Dunbar, R.I.M.; Shultz, S. |
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Title |
Understanding primate brain evolution |
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2007 |
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Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences |
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Philos Trans R Soc Lond B Biol Sci |
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362 |
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1480 |
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649-658 |
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We present a detailed reanalysis of the comparative brain data for primates, and develop a model using path analysis that seeks to present the coevolution of primate brain (neocortex) and sociality within a broader ecological and life-history framework. We show that body size, basal metabolic rate and life history act as constraints on brain evolution and through this influence the coevolution of neocortex size and group size. However, they do not determine either of these variables, which appear to be locked in a tight coevolutionary system. We show that, within primates, this relationship is specific to the neocortex. Nonetheless, there are important constraints on brain evolution; we use path analysis to show that, in order to evolve a large neocortex, a species must first evolve a large brain to support that neocortex and this in turn requires adjustments in diet (to provide the energy needed) and life history (to allow sufficient time both for brain growth and for 'software' programming). We review a wider literature demonstrating a tight coevolutionary relationship between brain size and sociality in a range of mammalian taxa, but emphasize that the social brain hypothesis is not about the relationship between brain/neocortex size and group size per se; rather, it is about social complexity and we adduce evidence to support this. Finally, we consider the wider issue of how mammalian (and primate) brains evolve in order to localize the social effects. |
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British Academy Centenary Research Project, School of Biological Sciences, University of Liverpool, Liverpool L69 7ZB, UK. rimd@liv.ac.uk |
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0962-8436 |
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PMID:17301028 |
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2099 |
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Dunbar, R.I.M.; Shultz, S. |
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Title |
Evolution in the Social Brain |
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2007 |
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Science |
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Science |
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317 |
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5843 |
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1344-1347 |
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The evolution of unusually large brains in some groups of animals, notably primates, has long been a puzzle. Although early explanations tended to emphasize the brain's role in sensory or technical competence (foraging skills, innovations, and way-finding), the balance of evidence now clearly favors the suggestion that it was the computational demands of living in large, complex societies that selected for large brains. However, recent analyses suggest that it may have been the particular demands of the more intense forms of pairbonding that was the critical factor that triggered this evolutionary development. This may explain why primate sociality seems to be so different from that found in most other birds and mammals: Primate sociality is based on bonded relationships of a kind that are found only in pairbonds in other taxa. |
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Equine Behaviour @ team @ |
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4243 |
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Pérez-Barbería, F.J.; Shultz, S.; Dunbar, R.I. |
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Evidence for coevolution of sociality and relative brain size in three orders of mammals |
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2007 |
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Evolution |
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61 |
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Equine Behaviour @ team @ Pérez-Barbería2007 |
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6221 |
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Pérez-Barbería, F.J.; Shultz, S.; Dunbar, R.I.M.; Janis, C. |
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Title |
Evidence For Coevolution Of Sociality And Relative Brain Size In Three Orders Of Mammals |
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2007 |
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Evolution |
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61 |
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12 |
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2811-2821 |
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Brain size, carnivores, coevolution, primates, sociality, ungulates |
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Abstract
As the brain is responsible for managing an individual's behavioral response to its environment, we should expect that large relative brain size is an evolutionary response to cognitively challenging behaviors. The “social brain hypothesis” argues that maintaining group cohesion is cognitively demanding as individuals living in groups need to be able to resolve conflicts that impact on their ability to meet resource requirements. If sociality does impose cognitive demands, we expect changes in relative brain size and sociality to be coupled over evolutionary time. In this study, we analyze data on sociality and relative brain size for 206 species of ungulates, carnivores, and primates and provide, for the first time, evidence that changes in sociality and relative brain size are closely correlated over evolutionary time for all three mammalian orders. This suggests a process of coevolution and provides support for the social brain theory. However, differences between taxonomic orders in the stability of the transition between small-brained/nonsocial and large-brained/social imply that, although sociality is cognitively demanding, sociality and relative brain size can become decoupled in some cases. Carnivores seem to have been especially prone to this. |
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doi: 10.1111/j.1558-5646.2007.00229.x |
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Equine Behaviour @ team @ |
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4781 |
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Saucier, D.M.; Shultz, S.R.; Keller, A.J.; Cook, C.M.; Binsted, G. |
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Sex differences in object location memory and spatial navigation in Long-Evans rats |
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2007 |
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Animal Cognition |
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Anim. Cogn. |
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In both humans and rodents, males typically excel on a number of tasks requiring spatial ability. However, human females exhibit advantages in memory for the spatial location of objects. This study investigated whether rats would exhibit similar sex differences on a task of object location memory (OLM) and on the watermaze (WM). We predicted that females should outperform males on the OLM task and that males should outperform females on the WM. To control for possible effects of housing environment, rats were housed in either complex environments or in standard shoebox housing. Eighty Long-Evans rats (40 males and 40 females) were housed in either complex (Complex rats) or standard shoebox housing (Control rats). Results indicated that males had superior performance on the WM, whereas females outperformed males on the OLM task, regardless of housing environment. As these sex differences cannot be easily attributed to differences in cognitive style related to linguistic processing of environmental features or to selection pressures related to the hunting gathering evolutionary prehistory of humans, these data suggest that sex differences in spatial ability may be related to traits selected for by polygynous mating strategies. |
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Canadian Centre for Behavioural Neuroscience, Department of Neuroscience, University of Lethbridge, 4401 University Dr., Lethbridge, AB, Canada, T1K 3M4, Deborah.Saucier@ULeth.ca |
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1435-9448 |
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PMID:17562087 |
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Equine Behaviour @ team @ |
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2391 |
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Shultz, S. |
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Are equid brains social? Exploring the evolution of equid social structure and social intelligence |
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Conference Article |
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2012 |
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Proceedings of the 2. International Equine Science Meeting |
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Proc. 2. Int. Equine. Sci. Mtg |
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in press |
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The living equids display a variety of different forms of social organisation; plains (Equus quagga) and mountain zebra (Equus zebra) associate in small, closed harems, whereas the asses and Grevy’s zebra (Equus grevyi) are found in looser, more ephemeral associations. Feral domestic horses appear to be somewhat intermediate: although stallions generally maintain harems, there is some movement of individuals between groups. This talk will use several statistical approached to explore evolutionary explanations for these differences. Firstly, we will explore the relationship between brain architecture and social organisation both among the equids and across all Perissodactyls. Equids have larger relative neocortices than other Perissodactyls; within the equids, species typically found in more stable groups have larger neocortices than equids in more unstable ephemeral groups. The strong relationship between group stability and brain size and architecture mirrors that found in other mammals, including primates. Thus, living in stable social groups consistently appears to impose cognitive demands across species. In order to understand the historical trajectory resulting in the relatively large, social brains found in some species, we then reconstruct the evolutionary pathway of social living in the equids. Finally, we discuss how we can use network theory to measure social structure and how these differences may impose different cognitive demands on individuals. |
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social brain hypothesis, Bayesian modelling, social networks, brain size, social evolution |
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Shultz, S. |
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Xenophon Publishing |
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Wald |
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Krueger, K. |
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978-3-9808134-26 |
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Equine Behaviour @ team @ |
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5557 |
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Shultz, S.; Dunbar, R.I.M. |
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Both social and ecological factors predict ungulate brain size |
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2006 |
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Proceedings. Biological Sciences / The Royal Society |
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Proc Biol Sci |
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273 |
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1583 |
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207-215 |
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Animals; Artiodactyla/*anatomy & histology/*physiology; Brain/*anatomy & histology/physiology; *Ecosystem; Organ Size; Perissodactyla/*anatomy & histology/*physiology; *Social Behavior |
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Among mammals, the members of some Orders have relatively large brains. Alternative explanations for this have emphasized either social or ecological selection pressures favouring greater information-processing capacities, including large group size, greater foraging efficiency, higher innovation rates, better invasion success and complex problem solving. However, the focal taxa for these analyses (primates, carnivores and birds) often show both varied ecological competence and social complexity. Here, we focus on the specific relationship between social complexity and brain size in ungulates, a group with relatively simple patterns of resource use, but extremely varied social behaviours. The statistical approach we used, phylogenetic generalized least squares, showed that relative brain size was independently associated with sociality and social complexity as well as with habitat use, while relative neocortex size is associated with social but not ecological factors. A simple index of sociality was a better predictor of both total brain and neocortex size than group size, which may indicate that the cognitive demands of sociality depend on the nature of social relationships as well as the total number of individuals in a group. |
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School of Biological Sciences, University of Liverpool, Biosciences Building, Crown Street, Liverpool L69 7ZB, UK. susanne.shultz@liv.ac.uk |
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0962-8452 |
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PMID:16555789 |
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2098 |
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Shultz, S.; Finlayson, L.V. |
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Large body and small brain and group sizes are associated with predator preferences for mammalian prey |
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2010 |
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Behavioral Ecology |
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Behav. Ecol. |
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21 |
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5 |
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1073-1079 |
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Predation is a major force in shaping biological communities, both over ecological and evolutionary timescales. In response to predation pressure, prey have evolved characteristics designed to mitigate predation pressure. We evaluated predator foraging biases in relation to prey characteristics across 16 vertebrate communities. We show that although predator biases vary, some prey traits are consistently associated with predator diet composition. Within their acceptable prey size range, predators show positive bias toward larger bodied prey, small-brained prey (controlling for body size), small group size, and terrestriality. Thus, whether predator foraging decisions are passive or active, predator choice exerts differential pressure on prey species according to prey characteristics. Predator biases also were positively associated with early age at maturity, supporting the role of mortality in driving life-history characteristics. These results support several theoretical models of predation including its role as a selective force driving evolutionary changes in life history, brain size and sociality, optimal diet theory, and antiapostatic predation. |
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10.1093/beheco/arq108 |
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Equine Behaviour @ team @ |
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5262 |
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Smolla, M.; Alem, S.; Chittka, L.; Shultz, S. |
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Copy-when-uncertain: bumblebees rely on social information when rewards are highly variable |
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2016 |
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Biology letters |
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Biol. Lett. |
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12 |
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6 |
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To understand the relative benefits of social and personal information use in foraging decisions, we developed an agent-based model of social learning that predicts social information should be more adaptive where resources are highly variable and personal information where resources vary little. We tested our predictions with bumblebees and found that foragers relied more on social information when resources were variable than when they were not. We then investigated whether socially salient cues are used preferentially over non-social ones in variable environments. Although bees clearly used social cues in highly variable environments, under the same conditions they did not use non-social cues. These results suggest that bumblebees use a 'copy-when-uncertain' strategy. |
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Equine Behaviour @ team @ |
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6198 |
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Stanley, C.; Shultz, S. |
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Mummy’s Boys: Sex Differential Maternal Offspring Relationships in Semi-feral Horses |
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2012 |
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Proceedings of the 2. International Equine Science Meeting |
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Proc. 2. Int. Equine. Sci. Mtg |
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in press |
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dispersal, Equus ferus caballus, social, maternal investment |
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In polygynous species with high reproductive skew in males, mothers often show differential investment between sons and daughters; however consistent sex differential investment has not been found by previous studies in horses. We investigated sex differences in mother-offspring relationships in nutritionally independent sub-adult semi-feral Carneddau Welsh mountain ponies Equus ferus caballus. Mothers and their sub-adult sons had consistently closer relationships than mothers and daughters. Stronger affiliative bonds between mothers and sons were quantified by their maintenance of closer proximity, higher rates of affiliative interactions and more frequent suckling bouts. These measures of affiliation were temporally associated with higher aggression levels directed towards sub-adults by other band members, particularly stallions. We suggest that aggression may serve as the proximate mechanism driving male dispersal in feral horses and that the stronger mother-son bond signals an attempt to delay their dispersal, highlighting conflict within the band concerning dispersal timing. Since males become increasingly central within the band over time, with mature stallions requiring excellent social skills in order to both acquire and keep a band of mares, we propose that delaying colts' dispersal allows for further development of these skills in a relatively safe environment. This additional investment is expected to maximise their reproductive success. This study illustrates how social network theory can be used to quantify individuals' social experiences, contributing to a greater understanding of the evolution of group living. It also gives us further insight into the mechanisms underlying dispersal in wild and semi-wild horse populations and how conflict often arises when individual needs differ. |
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Stanley, C. |
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Xenophon Publishing |
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Wald |
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Krueger, K. |
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Equine Behaviour @ team @ |
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5530 |
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