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Dunbar, R. I. M. (2007). Male and female brain evolution is subject to contrasting selection pressures in primates. BMC Biol, 5, 21.
Abstract: The claim that differences in brain size across primate species has mainly been driven by the demands of sociality (the “social brain” hypothesis) is now widely accepted. Some of the evidence to support this comes from the fact that species that live in large social groups have larger brains, and in particular larger neocortices. Lindenfors and colleagues (BMC Biology 5:20) add significantly to our appreciation of this process by showing that there are striking differences between the two sexes in the social mechanisms and brain units involved. Female sociality (which is more affiliative) is related most closely to neocortex volume, but male sociality (which is more competitive and combative) is more closely related to subcortical units (notably those associated with emotional responses). Thus different brain units have responded to different selection pressures.
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Brosnan, S. F., & de Waal, F. B. M. (2004). A concept of value during experimental exchange in brown capuchin monkeys, Cebus apella. Folia Primatol (Basel), 75(5), 317–330.
Abstract: We evaluated the response of brown capuchin monkeys to two differentially valued tokens in an experimental exchange situation akin to a simple barter. Monkeys were given a series of three tests to evaluate their ability to associate tokens with food, then their responses were examined in a barter situation in which tokens were either limited or unlimited. Capuchins did not perform barter in the typical sense, returning the tokens which were associated with the reward. However, females, but not males, showed a different response, preferring the higher-value token. This may indicate that they learned to prefer one token over the other rather than to associate the tokens with their specific rewards. This sex difference parallels previous findings of greater reciprocity in female brown capuchins than in males.
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Young, L. E., Rogers, K., & Wood, J. L. N. (2005). Left ventricular size and systolic function in Thoroughbred racehorses and their relationships to race performance. J Appl Physiol, 99(4), 1278–1285.
Abstract: Cardiac morphology in human athletes is known to differ, depending on the sports-specific endurance component of their events, whereas anecdotes abound about superlative athletes with large hearts. As the heart determines stroke volume and maximum O(2) uptake in mammals, we undertook a study to test the hypothesis that the morphology of the equine heart would differ between trained horses, depending on race type, and that left ventricular size would be greatest in elite performers. Echocardiography was performed in 482 race-fit Thoroughbreds engaged in either flat (1,000-2,500 m) or jump racing (3,200-6,400 m). Body weight and sex-adjusted measures of left ventricular size were largest in horses engaged in jump racing over fixed fences, compared with horses running shorter distances on the flat (range 8-16%). The observed differences in cardiac morphologies suggest that subtle differences in training and competition result in cardiac adaptations that are appropriate to the endurance component of the horses' event. Derived left ventricular mass was strongly associated with published rating (quality) in horses racing over longer distances in jump races (P < or = 0.001), but less so for horses in flat races. Rather, left ventricular ejection fraction and left ventricular mass combined were positively associated with race rating in older flat racehorses running over sprint (<1,408 m) and longer distances (>1,408 m), explaining 25-35% of overall variation in performance, as well as being closely associated with performance in longer races over jumps (23%). These data provide the first direct evidence that cardiac size influences athletic performance in a group of mammalian running athletes.
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McCrory, P., Turner, M., LeMasson, B., Bodere, C., & Allemandou, A. (2006). An analysis of injuries resulting from professional horse racing in France during 1991-2001: a comparison with injuries resulting from professional horse racing in Great Britain during 1992-2001. Br J Sports Med, 40(7), 614–618.
Abstract: BACKGROUND: It has been previously shown that professional jockeys suffer high rates of fatal and non-fatal injuries in the pursuit of their occupation. Little is known, however, about differences in injury rates between countries. AIM: To determine the rate of fatal and non-fatal injuries in flat and jump jockeys in France and to compare the injury rates with those in Great Britain and Ireland Method: Prospectively collected injury data on professional jockeys were used as the basis of the analysis. RESULTS: Limb fractures occur four times more often in both flat and jump racing in France than in Great Britain. Similarly dislocations are diagnosed 20 times more often in flat and three times more often in jump racing. This difference is surprising given that French jockeys have fewer falls per ride than their British counterparts in flat racing, although they do have more falls than the British in jump racing. Similarly concussion rates seem to be higher in French jockeys, although there may be a difference in the diagnostic methods used in the different countries. By contrast, soft tissue injuries account for a far smaller percentage of injuries than in Great Britain. CONCLUSION: There are striking differences in injury rates between countries which may be explained in part by a difference in track conditions-for example, harder tracks in France-or different styles of racing--for example, larger fields of horses per race in France.
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Thomas, K. E., Annest, J. L., Gilchrist, J., & Bixby-Hammett, D. M. (2006). Non-fatal horse related injuries treated in emergency departments in the United States, 2001-2003 (Vol. 40).
Abstract: OBJECTIVE: To characterise and provide nationally representative estimates of persons with non-fatal horse related injuries treated in American emergency departments. METHODS: The National Electronic Injury Surveillance System All Injury Program (NEISS-AIP) is a stratified probability sample comprising 66 hospitals. Data on injuries treated in these emergency departments are collected and reported. NEISS-AIP data on all types (horseback riding and otherwise) of non-fatal horse related injuries from 2001 to 2003 were analysed. RESULTS: An estimated 102,904 persons with non-fatal horse related injuries (35.7 per 100,000 population) were treated in American emergency departments each year from 2001 to 2003 inclusive. Non-fatal injury rates were higher for females (41.5 per 100,000) than for males (29.8 per 100,000). Most patients were injured while mounted on a horse (66.1%), commonly from falling or being thrown by the horse; while not mounted, injuries most often resulted from being kicked by the horse. The body parts most often injured were the head/neck region (23.2%), lower extremity (22.2%), and upper extremity (21.5%). The most common principal diagnoses were contusions/abrasions (31.4%) and fractures (25.2%). For each year that was studied, an estimated 11 502 people sustained traumatic brain injuries from horse related incidents. Overall, more than 11% of those injured were admitted to hospital. CONCLUSIONS: Horse related injuries are a public health concern not just for riders but for anyone in close contact with horses. Prevention programmes should target horseback riders and horse caregivers to promote helmet use and educate participants about horse behaviour, proper handling of horses, and safe riding practices.
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Danchin, E., Giraldeau, L. - A., Valone, T. J., & Wagner, R. H. (2004). Public information: from nosy neighbors to cultural evolution. Science, 305(5683), 487–491.
Abstract: Psychologists, economists, and advertising moguls have long known that human decision-making is strongly influenced by the behavior of others. A rapidly accumulating body of evidence suggests that the same is true in animals. Individuals can use information arising from cues inadvertently produced by the behavior of other individuals with similar requirements. Many of these cues provide public information about the quality of alternatives. The use of public information is taxonomically widespread and can enhance fitness. Public information can lead to cultural evolution, which we suggest may then affect biological evolution.
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Bergman, T. J., Beehner, J. C., Cheney, D. L., & Seyfarth, R. M. (2003). Hierarchical classification by rank and kinship in baboons. Science, 302(5648), 1234–1236.
Abstract: Humans routinely classify others according to both their individual attributes, such as social status or wealth, and membership in higher order groups, such as families or castes. They also recognize that people's individual attributes may be influenced and regulated by their group affiliations. It is not known whether such rule-governed, hierarchical classifications are specific to humans or might also occur in nonlinguistic species. Here we show that baboons recognize that a dominance hierarchy can be subdivided into family groups. In playback experiments, baboons respond more strongly to call sequences mimicking dominance rank reversals between families than within families, indicating that they classify others simultaneously according to both individual rank and kinship. The selective pressures imposed by complex societies may therefore have favored cognitive skills that constitute an evolutionary precursor to some components of human cognition.
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Weir, A. A. S., Chappell, J., & Kacelnik, A. (2002). Shaping of hooks in New Caledonian crows. Science, 297(5583), 981.
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Doligez, B., Danchin, E., & Clobert, J. (2002). Public information and breeding habitat selection in a wild bird population. Science, 297(5584), 1168–1170.
Abstract: According to the “public information” hypothesis, some animal species may monitor the current reproductive success of conspecifics to assess local habitat quality and to choose their own subsequent breeding site. To test this hypothesis experimentally, we manipulated two components of public information, the mean number of offspring raised locally (“quantity”) and their condition (“quality”), in the collared flycatcher Ficedula albicollis. Immigration rate decreased with local offspring quantity but did not depend on local offspring quality, suggesting that immigrants are deprived of information regarding local quality. Conversely, emigration rate increased both when local offspring quantity or quality decreased, suggesting that residents can use both components of public information.
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Clutton-Brock, T. H., Russell, A. F., Sharpe, L. L., Brotherton, P. N., McIlrath, G. M., White, S., et al. (2001). Effects of helpers on juvenile development and survival in meerkats. Science, 293(5539), 2446–2449.
Abstract: Although breeding success is known to increase with group size in several cooperative mammals, the mechanisms underlying these relationships are uncertain. We show that in wild groups of cooperative meerkats, Suricata suricatta, reductions in the ratio of helpers to pups depress the daily weight gain and growth of pups and the daily weight gain of helpers. Increases in the daily weight gain of pups are associated with heavier weights at independence and at 1 year of age, as well as with improved foraging success as juveniles and higher survival rates through the first year of life. These results suggest that the effects of helpers on the fitness of pups extend beyond weaning and that helpers may gain direct as well as indirect benefits by feeding pups.
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