Person: Wrangham, Richard
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Wrangham
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Wrangham, Richard
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Publication Equal, Similar, but Different: Convergent Bonobos and Conserved Chimpanzees(Harvard University Press, 2017-12-31) Hare, Brian; Wrangham, RichardA critical goal for human evolutionary biology is understanding when and how traits evolved in our ancestral lineage during the 6.5-9.3 million years since our split with the ancestors of chimpanzees and bonobos. Comparisons among humans and living apes are essential as they allow us to discriminate between traits that we share through common descent and those that have been modified since our split from Pan. This chapter suggests, based on the most recent quantitative comparisons of behavior, physiology, development, and cognition, that in many respects chimpanzees most closely approximate our last common ancestor (LCA) with chimpanzees and bonobos. It also suggests that bonobo and human psychology are similar in ways that indicate that cognitive evolution in the two species was guided by parallel mechanisms. The chapter discusses three main hypotheses: mosaic hypothesis, bonobo-like hypothesis, and chimpanzee-like hypothesis. The mosaic hypothesis claims that the relationship between traits in the living apes is not sufficiently consistent to suggest that one species is more representative of the LCA. The bonobo-like hypothesis has been suggested based partly on qualitative comparisons of behavior and cognition. The chimpanzee-like hypothesis conforms to evidence that bonobos are highly derived phenotypically relative to other nonhuman apes.Publication Applying Wet Sieving Fecal Particle Size Measurement to Frugivores: A Case Study of the Eastern Chimpanzee (Pan Troglodytes Schweinfurthii)(Wiley, 2017-04-04) Weary, Taylor; Wrangham, Richard; Clauss, MarcusFecal particle size (FPS) as quantified by wet sieving analysis is a measure of chewing efficiency relevant for the understanding of physiological adaptations and constraints in herbivores. FPS has not been investigated systematically in frugivores, and important methodological problems remain. In particular, food items that are not chewed may skew estimates of FPS. We address such methodological issues and also assess the influence of diet type and age on FPS in wild chimpanzees.Publication Citizen Science as a New Tool in Dog Cognition Research(Public Library of Science, 2015) Stewart, Laughlin; MacLean, Evan L.; Ivy, David; Woods, Vanessa; Cohen, Eliot; Rodriguez, Kerri; McIntyre, Matthew; Mukherjee, Sayan; Call, Josep; Kaminski, Juliane; Miklósi, Ádám; Wrangham, Richard; Hare, BrianFamily dogs and dog owners offer a potentially powerful way to conduct citizen science to answer questions about animal behavior that are difficult to answer with more conventional approaches. Here we evaluate the quality of the first data on dog cognition collected by citizen scientists using the Dognition.com website. We conducted analyses to understand if data generated by over 500 citizen scientists replicates internally and in comparison to previously published findings. Half of participants participated for free while the other half paid for access. The website provided each participant a temperament questionnaire and instructions on how to conduct a series of ten cognitive tests. Participation required internet access, a dog and some common household items. Participants could record their responses on any PC, tablet or smartphone from anywhere in the world and data were retained on servers. Results from citizen scientists and their dogs replicated a number of previously described phenomena from conventional lab-based research. There was little evidence that citizen scientists manipulated their results. To illustrate the potential uses of relatively large samples of citizen science data, we then used factor analysis to examine individual differences across the cognitive tasks. The data were best explained by multiple factors in support of the hypothesis that nonhumans, including dogs, can evolve multiple cognitive domains that vary independently. This analysis suggests that in the future, citizen scientists will generate useful datasets that test hypotheses and answer questions as a complement to conventional laboratory techniques used to study dog psychology.Publication Do Young Children Understand Relative Value Comparisons?(Public Library of Science, 2015) Benenson, Joyce; Markovits, Henry; Whitmore, Bjorn; Van, Christophe; Margolius, Sara; Wrangham, RichardMany forms of judgments, such as those used in economic games or measures of social comparison, require understanding relative value, as well as the more complex ability to make comparisons between relative values. To examine whether young children can accurately compare relative values, we presented children 4 to 7 years with simple judgments of relative value in two scenarios. Children then were asked to compare the relative values in the two scenarios. Results show that even the youngest children downgraded evaluations of a reward when another has a larger amount, indicating the ability to make relative value judgments. When asked to compare relative values however, only the oldest children were able to make these comparisons consistently. We then extended this analysis to economic game performance. Specifically, previous results using economic games suggest that younger children are more generous than older ones. We replicate this result, and then show that a simple change in procedure, based on the initial study, is sufficient to change young children’s choices. Our results strongly suggest that conclusions regarding young children’s pro-social motives based on relative value comparisons should be viewed cautiously.Publication Distribution of a Chimpanzee Social Custom Is Explained by Matrilineal Relationship Rather Than Conformity(Elsevier BV, 2016) Wrangham, Richard; Koops, Kathelijne; Machanda, Zarin; Worthington, Steven; Bernard, Andrew B.; Brazeau, Nicholas F.; Donovan, Ronan; Rosen, Jeremiah; Wilke, Claudia; Otali, Emily; Muller, Martin N.High-arm grooming is a form of chimpanzee grooming in which two individuals mutually groom while each raising one arm. Palm-to-palm clasping (PPC) is a distinct style of high-arm grooming in which the grooming partners clasp each other’s raised palms. In wild communities, samples of at least 100 observed dyads grooming with raised hands showed PPC frequencies varying from <5% (M group, Mahale) to >30% dyads grooming (Kanyawara, Kibale), and in a large free-ranging sanctuary group, the frequency reached >80% dyads (group 1, Chimfunshi) [1 ; 2]. Because between-community differences in frequency of PPC apparently result from social learning, are stable across generations, and last for at least 9 years, they are thought to be cultural, but the mechanism of transmission is unknown [2]. Here, we examine factors responsible for individual variation in PPC frequency within a single wild community. We found that in the Kanyawara community (Kibale, Uganda), adults of both sexes varied widely in their PPC frequency (from <10% to >50%) and did not converge on a central group tendency. However, frequencies of PPC were highly consistent within matrilines, indicating that individuals maintained lifelong fidelity to the grooming style of their mothers. Matrilineal inheritance of socially learned behaviors has previously been reported for tool use in chimpanzees [3] and in the vocal and feeding behavior of cetaceans [4 ; 5]. Our evidence indicates that matrilineal inheritance can be sufficiently strong in nonhuman primates to account for long-term differences in community traditions.Publication First Molar Eruption, Weaning, and Life History in Living Wild Chimpanzees(Proceedings of the National Academy of Sciences, 2013) Smith, Tanya; Machanda, Zarin; Bernard, Andrew B.; Donovan, Ronan M.; Papakyrikos, Amanda M.; Muller, Martin N.; Wrangham, RichardUnderstanding dental development in chimpanzees, our closest living relatives, is of fundamental importance for reconstructing the evolution of human development. Most early hominin species are believed to show rapid ape-like patterns of development, implying that a prolonged modern human childhood evolved quite recently. However, chimpanzee developmental standards are uncertain because they have never been based on living wild individuals. Furthermore, although it is well established that first molar tooth emergence (movement into the mouth) is correlated with the scheduling of growth and reproduction across primates broadly, its precise relation to solid food consumption, nursing behavior, or maternal life history is unknown. To address these concerns we conducted a photographic study of subadult chimpanzees (Pan troglodytes schweinfurthii) in Kanyawara, Kibale National Park, Uganda. Five healthy infants emerged their lower first molars (M1s) by or before 3.3 y of age, nearly identical to captive chimpanzee mean ages (∼3.2 y, n = 53). First molar emergence in these chimpanzees does not directly or consistently predict the introduction of solid foods, resumption of maternal estrous cycling, cessation of nursing, or maternal interbirth intervals. Kanyawara chimpanzees showed adult patterns of solid food consumption by the time M1 reached functional occlusion, spent a greater amount of time on the nipple while M1 was erupting than in the preceding year, and continued to suckle during the following year. Estimates of M1 emergence age in australopiths are remarkably similar to the Kanyawara chimpanzees, and recent reconstructions of their life histories should be reconsidered in light of these findings.Publication Social Influences on Inequity Aversion in Children(Public Library of Science, 2013-11-21) McAuliffe, Katherine; Blake, Peter R.; Kim, Grace; Wrangham, Richard; Warneken, FelixAdults and children are willing to sacrifice personal gain to avoid both disadvantageous and advantageous inequity. These two forms of inequity aversion follow different developmental trajectories, with disadvantageous inequity aversion emerging around 4 years and advantageous inequity aversion emerging around 8 years. Although inequity aversion is assumed to be specific to situations where resources are distributed among individuals, the role of social context has not been tested in children. Here, we investigated the influence of two aspects of social context on inequity aversion in 4- to 9-year-old children: (1) the role of the experimenter distributing rewards and (2) the presence of a peer with whom rewards could be shared. Experiment 1 showed that children rejected inequity at the same rate, regardless of whether the experimenter had control over reward allocations. This indicates that children’s decisions are based upon reward allocations between themselves and a peer and are not attempts to elicit more favorable distributions from the experimenter. Experiment 2 compared rejections of unequal reward allocations in children interacting with or without a peer partner. When faced with a disadvantageous distribution, children frequently rejected a smaller reward when a larger reward was visible, even if no partner would obtain the larger reward. This suggests that nonsocial factors partly explain disadvantageous inequity rejections. However, rejections of disadvantageous distributions were higher when the larger amount would go to a peer, indicating that social context enhances disadvantageous inequity aversion. By contrast, children rejected advantageous distributions almost exclusively in the social context. Therefore, advantageous inequity aversion appears to be genuinely social, highlighting its potential relevance for the development of fairness concerns. By comparing social and nonsocial factors, this study provides a detailed picture of the expression of inequity aversion in human ontogeny and raises questions about the function and evolution of inequity aversion in humans.Publication The “Domestication Syndrome” in Mammals: A Unified Explanation Based on Neural Crest Cell Behavior and Genetics(Genetics Society of America, 2014) Wilkins, Adam S.; Wrangham, Richard; Fitch, W. TecumsehCharles Darwin, while trying to devise a general theory of heredity from the observations of animal and plant breeders, discovered that domesticated mammals possess a distinctive and unusual suite of heritable traits not seen in their wild progenitors. Some of these traits also appear in domesticated birds and fish. The origin of Darwin’s “domestication syndrome” has remained a conundrum for more than 140 years. Most explanations focus on particular traits, while neglecting others, or on the possible selective factors involved in domestication rather than the underlying developmental and genetic causes of these traits. Here, we propose that the domestication syndrome results predominantly from mild neural crest cell deficits during embryonic development. Most of the modified traits, both morphological and physiological, can be readily explained as direct consequences of such deficiencies, while other traits are explicable as indirect consequences. We first show how the hypothesis can account for the multiple, apparently unrelated traits of the syndrome and then explore its genetic dimensions and predictions, reviewing the available genetic evidence. The article concludes with a brief discussion of some genetic and developmental questions raised by the idea, along with specific predictions and experimental tests.Publication Genetic differentiation and the evolution of cooperation in chimpanzees and humans(The Royal Society, 2011) Langergraber, K.; Schubert, Gary; Rowney, C.; Wrangham, Richard; Zommers, Z.; Vigilant, L.It has been proposed that human cooperation is unique among animals for its scale and complexity, its altruistic nature and its occurrence among large groups of individuals that are not closely related or are even strangers. One potential solution to this puzzle is that the unique aspects of human cooperation evolved as a result of high levels of lethal competition (i.e. warfare) between genetically differentiated groups. Although between-group migration would seem to make this scenario unlikely, the plausibility of the between-group competition model has recently been supported by analyses using estimates of genetic differentiation derived from contemporary human groups hypothesized to be representative of those that existed during the time period when human cooperation evolved. Here, we examine levels of between-group genetic differentiation in a large sample of contemporary human groups selected to overcome some of the problems with earlier estimates, and compare them with those of chimpanzees. We find that our estimates of between-group genetic differentiation in contemporary humans are lower than those used in previous tests, and not higher than those of chimpanzees. Because levels of between-group competition in contemporary humans and chimpanzees are also similar, these findings suggest that the identification of other factors that differ between chimpanzees and humans may be needed to provide a compelling explanation of why humans, but not chimpanzees, display the unique features of human cooperation.Publication Generation Times in Wild Chimpanzees and Gorillas Suggest Earlier Divergence Times in Great Ape and Human Evolution(Proceedings of the National Academy of Sciences, 2012) Langergraber, Kevin E.; Prufer, Kay; Rowney, Carolyn; Boesch, Christophe; Crockford, Catherine; Fawcett, Katie; Inoue, Eiji; Inoue-Muruyama, Miho; Mitani, John C.; Muller, Martin N.; Robbins, Martha M.; Schubert, Grit; Stoinski, Tara S.; Viola, Bence; Watts, David; Wittig, Roman M.; Wrangham, Richard; Zuberbuhler, Klaus; Paabo, Svante; Vigilant, LindaFossils and molecular data are two independent sources of information that should in principle provide consistent inferences of when evolutionary lineages diverged. Here we use an alternative approach to genetic inference of species split times in recent human and ape evolution that is independent of the fossil record. We first use genetic parentage information on a large number of wild chimpanzees and mountain gorillas to directly infer their average generation times. We then compare these generation time estimates with those of humans and apply recent estimates of the human mutation rate per generation to derive estimates of split times of great apes and humans that are independent of fossil calibration. We date the human–chimpanzee split to at least 7–8 million years and the population split between Neanderthals and modern humans to 400,000–800,000 y ago. This suggests that molecular divergence dates may not be in conflict with the attribution of 6- to 7-million-y-old fossils to the human lineage and 400,000-y-old fossils to the Neanderthal lineage.