Adaptation
Nonlinear detection of paleoclimate-variability transitions possibly related to human evolution
Jonathan Donges et al.
Proceedings of the National Academy of Sciences, 20 December 2011, Pages 20422-20427
Abstract:
Potential paleoclimatic driving mechanisms acting on human evolution present an open problem of cross-disciplinary scientific interest. The analysis of paleoclimate archives encoding the environmental variability in East Africa during the past 5 Ma has triggered an ongoing debate about possible candidate processes and evolutionary mechanisms. In this work, we apply a nonlinear statistical technique, recurrence network analysis, to three distinct marine records of terrigenous dust flux. Our method enables us to identify three epochs with transitions between qualitatively different types of environmental variability in North and East Africa during the (i) Middle Pliocene (3.35-3.15 Ma B.P.), (ii) Early Pleistocene (2.25-1.6 Ma B.P.), and (iii) Middle Pleistocene (1.1-0.7 Ma B.P.). A deeper examination of these transition periods reveals potential climatic drivers, including (i) large-scale changes in ocean currents due to a spatial shift of the Indonesian throughflow in combination with an intensification of Northern Hemisphere glaciation, (ii) a global reorganization of the atmospheric Walker circulation induced in the tropical Pacific and Indian Ocean, and (iii) shifts in the dominating temporal variability pattern of glacial activity during the Middle Pleistocene, respectively. A reexamination of the available fossil record demonstrates statistically significant coincidences between the detected transition periods and major steps in hominin evolution. This result suggests that the observed shifts between more regular and more erratic environmental variability may have acted as a trigger for rapid change in the development of humankind in Africa.
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Barış Özener
Evolution and Human Behavior, forthcoming
Abstract:
Recently, Weston et al. (2004; Wide faces or large canines? The attractive versus the aggressive primate. Proceedings of the Royal Society of London, Series B, 271, 416-419) found that facial width-to-height ratio (WHR) is a sexually dimorphic characteristic in humans; males have higher facial WHR than females. Following this study, Carré et al. (2008; In your face: facial metrics predict aggressive behavior in the laboratory and in varsity and professional hockey players. Proceedings of the Royal Society of London, Series B, 275, 2651-2656) found that individual differences in facial WHR accounted for a significant proportion of the variance in aggressive behavior of men, but not women. I tested these two hypotheses in a sample of 470 Turkish university students. Facial WHR was measured from frontal photographs. I also measured the aggressiveness level of 212 individuals using the Buss and Perry aggressiveness questionnaire. The mean facial WHR (and standard deviation) was 1.89±0.12 for males and 1.91±0.11 for females. There was no relationship between facial WHR and the self-reported aggressive behavior for either sex. The facial WHR is not a sexually dimorphic characteristic (at least) for Turkish people, and it does not appear to be associated with self-reported trait aggression.
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Native Americans experienced a strong population bottleneck coincident with European contact
Brendan O'Fallon & Lars Fehren-Schmitz
Proceedings of the National Academy of Sciences, forthcoming
Abstract:
The genetic and demographic impact of European contact with Native Americans has remained unclear despite recent interest. Whereas archeological and historical records indicate that European contact resulted in widespread mortality from various sources, genetic studies have found little evidence of a recent contraction in Native American population size. In this study we use a large dataset including both ancient and contemporary mitochondrial DNA to construct a high-resolution portrait of the Holocene and late Pleistocene population size of indigenous Americans. Our reconstruction suggests that Native Americans suffered a significant, although transient, contraction in population size some 500 y before the present, during which female effective size was reduced by ∼50%. These results support analyses of historical records indicating that European colonization induced widespread mortality among indigenous Americans.
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Piotr Sorokowski et al.
Journal of Cross-Cultural Psychology, January 2012, Pages 32-37
Abstract:
In Western societies women prefer relatively taller men as potential partners, whereas men prefer women to be slightly shorter than them. Here we report data on relative height preferences in a traditional ethnic group, i.e. the Himba, in which men and women do not show such a strong preference. Thus our data challenges the view of a universal preference for taller men, by suggesting that height preferences may be influenced by environmental and ecological conditions.
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Cultural diversification promotes rapid phenotypic evolution in Xavánte Indians
Tábita Hünemeier et al.
Proceedings of the National Academy of Sciences, forthcoming
Abstract:
Shifts in social structure and cultural practices can potentially promote unusual combinations of allele frequencies that drive the evolution of genetic and phenotypic novelties during human evolution. These cultural practices act in combination with geographical and linguistic barriers and can promote faster evolutionary changes shaped by gene-culture interactions. However, specific cases indicative of this interaction are scarce. Here we show that quantitative genetic parameters obtained from cephalometric data taken on 1,203 individuals analyzed in combination with genetic, climatic, social, and life-history data belonging to six South Amerindian populations are compatible with a scenario of rapid genetic and phenotypic evolution, probably mediated by cultural shifts. We found that the Xavánte experienced a remarkable pace of evolution: the rate of morphological change is far greater than expected for its time of split from their sister group, the Kayapó, which occurred around 1,500 y ago. We also suggest that this rapid differentiation was possible because of strong social-organization differences. Our results demonstrate how human groups deriving from a recent common ancestor can experience variable paces of phenotypic divergence, probably as a response to different cultural or social determinants. We suggest that assembling composite databases involving cultural and biological data will be of key importance to unravel cases of evolution modulated by the cultural environment.
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Deference in Indians' decision making: Introjected goals or injunctive norms?
Krishna Savani, Michael Morris & N.V.R. Naidu
Journal of Personality and Social Psychology, forthcoming
Abstract:
We examine the claim that Indians are more likely than Americans to act deferentially in the presence of authority figures and explore 2 possible psychological mechanisms for this cultural difference: introjected goals and injunctive norms. Studies 1 and 2 showed that after reflecting upon an authority's expectations, Indians were more likely than Americans to make clothing and course choices consistent with the authority's expectations, but there was no such cultural difference for peers' expectations. Study 3 showed that merely activating the concept of authority figures, without highlighting specific expectations, was sufficient to influence Indians' choices but not their evaluations. Examining a more basic distinction underlying introjected goals versus injunctive norms, Study 4 showed that authority primes influenced Indians' sense of what they should do but not what they want to do. Study 5 showed that, inconsistent with the internalized goal mechanism, the effect of explicit authority primes did not increase after brief delays. However, Indian participants who were less likely to accommodate to the salient authority experienced more guilt across delay conditions, which supported the injunctive norms mechanism. The findings suggest that manipulating injunctive norms can be an effective means for inducing or eliminating deferential behaviors in Indian settings.
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Culture and accountability in negotiation: Recognizing the importance of in-group relations
Wu Liu, Ray Friedman & Ying-Yi Hong
Organizational Behavior and Human Decision Processes, forthcoming
Abstract:
We extend Gelfand and Realo's (1999) argument that accountability motivates negotiators from relationally-focused cultures to use a more pro-relationship approach during negotiations. Our research shows that the effect they predict is found only when the other negotiating partner is an in-group member. Specifically, in two studies involving participants from China (a relationally-focused culture) and the US (a less relationally-focused culture), we found that only when negotiating with an in-group member are Chinese participants under high accountability more likely to use a pro-relationship approach than those under low accountability. Consequently, the differences between Chinese and American participants in the use of a pro-relationship approach occur only when they negotiate with an in-group member under high accountability. The strong attention to relationships, however, results in higher fixed-pie perceptions and lower joint gains. The implications of our findings for theory and practice are discussed.
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Peter Smith et al.
Journal of Cross-Cultural Psychology, January 2012, Pages 135-150
Abstract:
The purpose of the study was to investigate the cultural specificity of guanxi, wasta, and jeitinho, each of which has been identified as an indigenous process of informal influence. Students in Brazil, China, Lebanon, and the United Kingdom were presented with three scenarios derived from each of the nations sampled. They rated the extent to which each scenario was representative of the locally indigenous process, the typicality for their culture of the events portrayed in the scenarios, and the extent to which these interpersonal exchanges were perceived positively. While each type of scenario was perceived as representative and typical in its culture of origin, each was also perceived as somewhat typical by respondents in additional locations. Informal influence processes may vary between cultures more in frequency than in quality. Rated scenario positivity was significantly predicted by respondents' values. The United Kingdom-based process of "pulling strings" was rated as typical in all locations and was more positively evaluated than the other influence processes by all respondents. It is concluded that in addition to the pragmatic value of these concepts locally, their comparative testing can contribute to the development of culture-general models of social influence processes.
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Miki Ben-Dor et al.
PLoS ONE, December 2011, e28689
Abstract:
The worldwide association of H. erectus with elephants is well documented and so is the preference of humans for fat as a source of energy. We show that rather than a matter of preference, H. erectus in the Levant was dependent on both elephants and fat for his survival. The disappearance of elephants from the Levant some 400 kyr ago coincides with the appearance of a new and innovative local cultural complex - the Levantine Acheulo-Yabrudian and, as is evident from teeth recently found in the Acheulo-Yabrudian 400-200 kyr site of Qesem Cave, the replacement of H. erectus by a new hominin. We employ a bio-energetic model to present a hypothesis that the disappearance of the elephants, which created a need to hunt an increased number of smaller and faster animals while maintaining an adequate fat content in the diet, was the evolutionary drive behind the emergence of the lighter, more agile, and cognitively capable hominins. Qesem Cave thus provides a rare opportunity to study the mechanisms that underlie the emergence of our post-erectus ancestors, the fat hunters.
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Angela Leung et al.
Journal of Cross-Cultural Psychology, January 2012, Pages 46-52
Abstract:
When the relative contribution of the self and the group to a group success is unclear, Americans tend to exhibit a self-serving bias (rewarding the self more than what the self deserves), whereas the Chinese tend to exhibit an other-serving bias (rewarding the group more than the group deserves). In a study comparing the reward allocation biases of Americans and Chinese in different group outcome conditions, the authors showed that the abovementioned cultural difference is found (a) only for culturally congruent success experience (attaining approach goals for Americans and avoidance goals for Chinese) and (b) among individuals who are motivated by the need for cognitive closure to exhibit culturally typical responses. This finding has important implications for understanding the dynamic nature of cultural influences on social behaviors.
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Avoidance of overheating and selection for both hair loss and bipedality in hominins
Graeme Ruxton & David Wilkinson
Proceedings of the National Academy of Sciences, forthcoming
Abstract:
Two frequently debated aspects of hominin evolution are the development of upright bipedal stance and reduction in body hair. It has long been argued, on the basis of heat-balance models, that thermoregulation might have been important in the evolution of both of these traits. Previous models were based on a stationary individual standing in direct sunlight; here we extend this approach to consider a walking hominin, having argued that walking is more thermally challenging than remaining still. Further, stationary activities may be more compatible with shade seeking than activities (such as foraging) involving travel across the landscape. Our model predictions suggest that upright stance probably evolved for nonthermoregulatory reasons. However, the thermoregulatory explanation for hair loss was supported. Specifically, we postulate progressive hair loss being selected and this allowing individuals to be active in hot, open environments initially around dusk and dawn without overheating. Then, as our ancestors' hair loss increased and sweating ability improved over evolutionary time, the fraction of the day when they could remain active in such environments extended. Our model suggests that only when hair loss and sweating ability reach near-modern human levels could hominins have been active in the heat of the day in hot, open environments.
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Leslie Zebrowitz et al.
Journal of Cross-Cultural Psychology, January 2012, Pages 119-134
Abstract:
The authors examined the generalizability of first impressions from faces previously documented in industrialized cultures to the Tsimane' people in the remote Bolivian rainforest. Tsimane' as well as U.S. judges showed within-culture agreement in impressions of attractiveness, babyfaceness, and traits (healthy, intelligent/knowledgeable, dominant/respected, and sociable/warm) of own-culture faces. Both groups also showed within-culture agreement for impressions of other-culture faces, although it was weaker than for own-culture faces, particularly among Tsimane' judges. Moreover, there was between-culture agreement, particularly for Tsimane' faces. Use of facial attractiveness to judge traits contributed to agreement within and between cultures but did not fully explain it. Furthermore, Tsimane', like U.S., judges showed a strong attractiveness halo in impressions of faces from both cultures as well as the babyface stereotype, albeit more weakly. In addition to cross-cultural similarities in trait impressions from faces, supporting a universal mechanism, some effects were moderated by perceiver and face culture, consistent with perceiver attunements conditioned by culturally specific perceptual learning.
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Hunter-gatherers and other primates as prey, predators, and competitors of snakes
Thomas Headland & Harry Greene
Proceedings of the National Academy of Sciences, forthcoming
Abstract:
Relationships between primates and snakes are of widespread interest from anthropological, psychological, and evolutionary perspectives, but surprisingly, little is known about the dangers that serpents have posed to people with prehistoric lifestyles and nonhuman primates. Here, we report ethnographic observations of 120 Philippine Agta Negritos when they were still preliterate hunter-gatherers, among whom 26% of adult males had survived predation attempts by reticulated pythons. Six fatal attacks occurred between 1934 and 1973. Agta ate pythons as well as deer, wild pigs, and monkeys, which are also eaten by pythons, and therefore, the two species were reciprocally prey, predators, and potential competitors. Natural history data document snake predation on tree shrews and 26 species of nonhuman primates as well as many species of primates approaching, mobbing, killing, and sometimes eating snakes. These findings, interpreted within the context of snake and primate phylogenies, corroborate the hypothesis that complex ecological interactions have long characterized our shared evolutionary history.