Center for Behavior, Evolution, and Culture

Bruce Bridgeman - Treading a Slippery Slope: Slant Perception in Near and Far Space
2009-10-12 00:00 (America/Los_Angeles)
Bruce Bridgeman: UC Santa Cruz Department of PsychologyEstimation of slope is an everyday tool for navigating the external world. Previous studies have found that slopes are overestimated more greatly with a verbal than with a proprioceptive measure. Since some neurons in the premotor cortex respond differently to objects within armâ€™s reach, we hypothesized that slope estimation may also be affected by neural pathways that respond differently to identical visual information at different distances. Alternatively, vision may be warning us about the greater effort required to walk up a slope. Verbal estimates greatly overestimated the actual slope, and increased logarithmically with distance from the participant, contradicting both theories. Proprioceptive estimates were more accurate. When participants experience a slope directly by walking up and down a hill prior to making estimates, their estimates remain unchanged. Increases in perceived slope with distance depend upon range of the segment judged, not length of the segment. The results can be interpreted as an implicit slope, previously measured only in darkness, modulated by depth cues available at near distances. http://www.bec.ucla.edu/slopes09.pdf

Greg Hickok - On the nature of auditory-motor interaction in speech processing: implications for the interpretation of mirror neurons and beyond
2009-10-05 00:00
Greg Hickok: UC Irvine Cognitive Sciences & Center for Cognitive NeuroscienceThere are two ideas regarding how auditory and motor speech systems interact in language processing. A popular view in the neuroscience community is that motor systems play an important role in the perception of speech. This is an old idea that has been largely (if not completely) abandoned on empirical grounds by the speech science community. However, the discovery of mirror neurons in the macaque brain has resurrected the hypothesis among neuroscientists. The other idea regarding auditory-motor interaction comes out of the motor control literature which has provided compelling evidence that the auditory system plays an important role in speech production. I will review the evidence, current and past, for these two hypotheses and conclude (i) the motor system is not necessary for speech perception, (ii) the motor system may be able to exert a top-down influence on auditory speech perception system but the evidence remains inconclusive and even if real the effects are relatively minor, (iii) there is strong evidence for the reverse relation, that auditory systems play a critical role in aspects of speech production. I will also review a number of fMRI and lesion studies aimed at mapping the cortical circuit supporting sensory-motor interaction in speech processing.

Aaron Sell - An evolutionary-computational model of human anger
2009-09-28 00:00
Aaron Sell: UCSB Department of PsychologyAnger can be understood as a cognitive mechanism designed by natural selection to negotiate conflicts of interest in ways similar to, but distinct from, non-human animal conflict. The Recalibrational Theory of anger uses an evolutionary biological framework to predict the major features of anger and explain their computational structure by reference to this function. Datasets collected from five distinct cultures address the major features of anger including under what conditions anger is evoked, when aggression is used by the anger system, which individuals set lower thresholds for anger and aggression, why and how anger triggers modifications of the face and voice, and how one predicts and explains the computational structure of anger-based arguments. The data demonstrate that anger is a well-designed system for recalibrating targets in ways that minimize immediate and future costs resulting from conflicts of interest.http://www.bec.ucla.edu/SellTalk.pdf

Devesh Rustagi - Conditional Cooperation Norm, Altruistic Punishment, and Participatory Forest Management in Ethiopia
2009-06-03 00:00
Devesh Rustagi: Swiss Federal Institute of Technology, Zurich – Department of Environmental Policy and EconomicsRecent research suggests that the power of conditional cooperation norm and punishment of norm violators in sustaining cooperation depends on behavioral type composition of a group, which has been shown, experimentally, to have a predictive effect on cooperation outcome. However, because the existing evidence is exclusively based on experiments with a handful of students from the industrialized west, fundamental questions on the occurrence of this evidence across cultures, in a real world setting, and itâ€™s policy relevance remain unanswered. Here, we report results from experiments and surveys with 679 members belonging to 49 forest user societies engaged in the management of common property forests in Ethiopia. We find that, first, 35 % members behave as conditional cooperators. Second, the share of conditional cooperators in a society has a significantly positive effect on the societyâ€™s forest management outcome, even when we control for structural determinants of cooperation. Third, conditional cooperators use costly monitoring as a mechanism to achieve a better forest outcome. The unique field settings allow us to generate this evidence in conditions where endogenous group formation, high migration and reverse causality have been ruled out. Our findings provide empirical support to the models of punishment and cultural group selection.

Ruth Mace - Cultural Evolution and the Behavioural Ecology of Fertility Decline
2009-06-01 00:00
Ruth Mace: University College London Department of AnthropologyA behavioural ecological approach to human birth rates suggests they should vary according to the costs of raising children to adulthood. Demographers and most other social scientists are sceptical of this view, not least because birth rates are generally lowest in the wealthiest countries; most favour arguments based on cultural changes and cultural influences. I will argue that evolutionary arguments based on costs and benefits and on cultural influence are not mutually exclusive and that variation in birth rates both within populations and also across populations can be understood in terms of different levels of parental investment and different constraints on parents. I will draw on data from Kenya, Ethiopia, the Gambia and the UK to illustrate these points.

Athena Aktipis - Walking Away from the Haystack: Conditional Movement Favors the Evolution of Cooperation in Groups
2009-05-27 00:00
Athena Aktipis: University of Arizona Department of Ecology and Evolutionary BiologyModels such as Maynard Smithâ€™s Haystack model have shown that high rates of movement (i.e., migration, mixing, dispersal) undermine the evolution of cooperation. However, these models generally assume that movement is unconditional. The present model replaces the assumption of unconditional movement with conditional movement; individuals stay in groups that provide higher returns (by virtue of having more cooperators), and â€˜Walk Awayâ€™ from groups providing low returns. Implementing this conditional movement rule generates a number of findings including: 1) when individuals have high thresholds, corresponding to low tolerance for defectors, this lead to selection for cooperation, 2) high thresholds lead to high rates of movement initially and lower rates of movement after selection for cooperators, and 3) population structure becomes more stable after selection increases the proportion of cooperators in the population. These findings challenge the standard view derived from Maynard Smithâ€™s Haystack model and others that high rates of movement undermine selection for cooperation. In contrast, the current model demonstrates that high rates of conditional movement can be associated with stronger selection for cooperation. These results show that high rates of migration observed in nature are not prohibitive for the evolution of cooperation, as standard group selection models have assumed.http://www.bec.ucla.edu/AktipisWalkingAwayTextAndFigs.doc

Nina Jablonski - The Evolution and Significance of Human Nakedness
2009-05-20 00:00
Nina Jablonski: Penn State Department of AnthropologyHumans are distinguished from other primates by being functionally hairless over most of their bodies. This condition evolved because hairlessness facilitated cooling of the body by sweating. The evaporative cooling made possible by sweating results in whole-body cooling of blood flowing in superficial vessels, and the maintenance of constant brain temperature. The combination of anatomical, physiological, and new genetic information pertaining to the structure and function human skin have helped to â€œlay bareâ€ the evolution of human hairlessness and sweatiness. Hairlessness had major consequences for the evolution of skin pigmentation and the communication of visual information and signals through elaborated facial expressions and, later, body painting and decoration.http://www.bec.ucla.edu/JablonskiTalk.pdf

Daniel Geschwind - Transcriptome Organization in Human and Primate Brain: Connecting Genes to Brain to Cognition and Behavior
2009-05-18 00:00
Daniel Geschwind: UCLA Departments of Human Genetics, Neurology, and PsychiatryWe are interested in understanding how genes influence human cognition and behavior, leading to unique human cognitive specializations, such as language. Advances in molecular and statistical genetics now allow us to identify genes that may be responsible for the emergence of some of these human cognitive features. But convergent approaches relying on data from several levels are necessary to understand a particular geneâ€™s relationship to brain structure and function. To do this, we have undertaken a multidisciplinary approach involving the study of human diseases affecting these features, such as autism, as well as human brain evolution. We have begun to develop methods that try to take into account the systems level organization of gene expression (the transcriptome), and applied these to large scale data sets. This has revealed a previously unrecognized organization to the transcriptional program in brain, which provides a framework on which to understand adaptive changes in gene expression on the human lineage.http://www.bec.ucla.edu/OldhamEtAlNatureNeuroscience.pdf

Joseph Manson - Adherence to Conversational Norms in Interactions Among Strangers: Effects on Cooperation and Expectations of Cooperation
2009-05-11 00:00
Joseph Manson: UCLA Department of AnthropologySeveral studies have shown that, following brief interactions among strangers, subjects perform better than chance at predicting whether their co-subjects will defect in a one-shot Prisonerâ€™s Dilemma Game (PDG). However, previous work did not explore how such predictive accuracy was possible. Theoretical work suggests that adherence to â€œarbitraryâ€ norms serves a signaling function that allows individuals to assort so as to maximize coordination and cooperative efficiency. One set of norms, documented by Conversation Analysis (CA), concerns the details of face-to-face interaction, such as respecting interlocutorsâ€™ rights to complete each turn constructional unit (TCU). We hypothesized that Defection in a PDG and predictions of co-subjectsâ€™ Defections would be more likely vis-Ã -vis unfamiliar interlocutors who violated conversational norms at higher frequencies. We videotaped short conversations among same-sex triads of previously unacquainted university students who were naÃ¯ve to the impending PDG. We then separated participants and directed each of them to (a) play a one-shot PDG with each of their two co-participants and to predict one anotherâ€™s play decisions and (b) complete the Levenson Self-Report Psychopathy Scale (LSRP) along with some demographic questions. From each videotaped conversation, a mean of 3.93 min was transcribed using CA methods. Subjects chose to cooperate in 67.7% of decisions, comparable to previous studies of face-to-face interaction. However, participants performed no better than chance at predicting one anotherâ€™s game play decisions. Nonetheless, personality and conversational behavior were related to one another and to objective outcomes like game play and earnings, in both expected and unexpected ways. We discuss these results with reference to the co-evolution of human cultural variation, cultural capacities and social judgment mechanisms.

Scott Johnson - Mental Rotation in Adults and Infants: A Sex Difference
2009-05-04 00:00
Scott Johnson: UCLA Department of PsychologyMental rotation (MR) is the process by which people imagine how an object would look when rotated into a different orientation in space; it may be related to performance on tasks like perspective-taking and navigation. Men typically perform faster and more accurately than women on MR tasks. Known influences on MR performance in adults are both biological (e.g., exposure to testosterone) and experiential (e.g., practice at spatial tasks), raising vital questions about the developmental origins of MR. Until recently, developmental studies were limited to children 4 years and older. This talk will present evidence that sex differences in MR performance are present far earlier, and can be observed in preverbal infants. I will also discuss the influence of task demands on MR in infants, and the possible biological and environmental contributions to performance that may shed light on the intersection of visual/motor skills and mental imagery of 3D objects early in life.http://www.bec.ucla.edu/MooreJohnson2008.pdf

Paul Mellars - Rethinking Modern Human Behavioural Origins and Dispersal: Archaeological and Genetic Perspectives
2009-04-29 00:00
Paul Mellars: University of Cambridge Department of ArchaeologyResearch over the past ten years in both DNA studies and archaeology has provided some remarkable new insights into the origins of biologically and behaviourally modern human populations, and their widespread dispersal from Africa to the rest of the world around 60,000 years ago.
The combination of DNA studies and recent finds of skeletal remains show that essentially ‘modern’ humans had emerged in Africa by at least 150-200,000 years ago, and subsequently spread from Africa into both Asia and Europe around 55-60,000 years ago, where they rapidly replaced the pre-existing “archaic” populations (including the Eurasian Neanderthals) within a matter of a few thousand years.
This talk will focus specifically on the patterns of dispersal of biologically and behaviourally modern humans from Africa, and the nature of the cultural and behavioural adaptations which made this dispersal possible. The aim will be to compare and integrate evidence from both genetic (i.e. DNA) studies and the recent spate of new archaeological discoveries in Africa and elsewhere. The talk will focus on the two questions of (a) why there was a delay of around 100,000 years between the initial emergence of modern Homo sapiens in Africa and their subsequent dispersal to the rest of the world; and (b) what range of behavioural innovations and adaptations allowed the widespread geographical dispersal of modern humans into a range of new and sharply contrasting environments, and the rapid replacement of the pre-existing ‘archaic’ populations in these regions, within such a short space of time. How far these behavioural innovations can be attributed to a major neurological change, and how far to simple cumulative ‘feedback’ processes of technological, social and other behavioural changes remains a central and critical question for future research.http://www.bec.ucla.edu/MellarsDispersalModel.pdf

Jenessa Shapiro - Perceiving White Norms: Ironic Effects in Blacks' versus Whites' Judgments of Minority Targets
2009-04-27 00:00
Jenessa Shapiro: UCLA Department of PsychologyConformity to a perceived norm is a common strategy used to gain the approval of one’s interaction partners. Identifying a group norm is ordinarily relatively simple. However, this task may be especially difficult when the norm is held by a group to which one does not belong, as is the case in intergroup interactions. In contemporary American society, Whites tend to believe that norms condemning public expressions of racial prejudices are pervasive (e.g., Dovidio & Gaertner, 1986). In contrast, Black Americans tend to view normative White behavior as prejudicial against themselves and other minority groups (e.g., Neimann, Jennings, Rozelle, Baxter, & Sullivan, 1994). The present research examined some ironic implications of this divergent perception of White prejudice-relevant norms. In one study, when evaluations of a Native American job candidate were to be made public to an unfamiliar group of White males upon whom participants were dependent, White men expressed less prejudice whereas Black men expressed greater prejudice, relative to when these responses remained private. In contrast, White and Black females expressed no prejudice when their evaluations were to be public to White females, although Black females expressed generally more favorable judgments of both White and Native American candidates. Follow-up studies support the hypothesis that differential inferences about White prejudice norms underlie this pattern of findings: The public judgments made by Black males (compensatory conformity) and Black females (compensatory pleasantness) can be seen as strategies aimed at reducing the likelihood that they themselves will be discriminated against in an intergroup interaction.

Edouard Machery - Did Morality Really Evolve?
2009-04-20 00:00
Edouard Machery: University of Pittsburgh Department of History and Philosophy of ScienceThat morality evolved is a commonplace among evolutionary biologists, psychologists, and anthropologists. In this talk, I will however argue that biologists, psychologists, and anthropologists have failed to pay enough attention to the differences between three distinct interpretations of the hypothesis that morality evolved: (1) some components of moral cognition (e.g., some particular emotions, concepts, or norms) evolved, (2) a capacity to grasp and be motivated by norms in general evolved, and (3) a capacity to grasp and be motivated by a distinctive type of norms evolved. Under the first two interpretations, it is fairly uncontroversial that morality evolved, while under the third and most interesting interpretation, the hypothesis that morality evolved is empirically unsupported. Philosophical implications in ethics will be incidentally considered.http://www.bec.ucla.edu/MacheryEvolutionOfMorality.pdf

Barbara KÃ¶nig - Cooperation and Social Selection - A Case Study of Communal Nursing in House Mice
2009-04-15 00:00
Barbara KÃ¶nig: University of Zurich Institute of ZoologyIn addition to sexual selection, selection resulting from social interactions in contexts other than mating can be a potent evolutionary force. Such social selection processes are facilitated whenever individual fitness varies as a result of any form of social interactions. The choice of social partners for communal care of young is such a situation in which interactants potentially experience fitness variance. We combine lab experiments with field data to investigate the existence and impact of female social partner choice and the potential for social selection to occur in the communally breeding wild house mouse (Mus domesticus). Female house mice display non-random preferences, and social partner choice yields significant fitness benefits. This suggests that interactions among females are subject to social selection processes, driving the evolution of female traits.http://www.bec.ucla.edu/Konig.pdf

Naomi Eisenberger - Why Rejection Hurts: Examining the Shared Mechanisms Underlying Physical and Social Pain
2009-04-13 00:00
Naomi Eisenberger: UCLA Department of PsychologyNumerous languages characterize â€˜social pain,â€™ the feelings resulting from social rejection or loss, with words typically reserved for describing physical pain (â€œbroken hearts,â€ â€œhurt feelingsâ€) and perhaps for good reason. It has been suggested that, in mammalian species, the social attachment system borrowed the computations of the physical pain system in order to prevent the potentially harmful consequences of social separation. In this talk, I will use a combination of behavioral and neuroimaging methodologies to explore the notion that physical and social pain rely on overlapping neural and experiential processes. Specifically, I will examine: 1) whether social pain activates pain-related neural circuitry, 2) whether individual differences in sensitivity to one kind of pain relate to individual differences in sensitivity to the other (e.g. Are individuals who are more sensitive to physical pain also more sensitive to social pain?), and 3) whether factors that up- or down-regulate one type of pain affect the other in a similar manner (e.g., Can physical painkillers reduce social pain?).

Joseph Henrich - The Evolution of Cultural Adaptations: Fijian Food Taboos Protect Against Dangerous Marine Toxins
2009-04-06 00:00
Joseph Henrich: University of British Columbia Departments of Psychology and EconomicsThis talk will first develop an evolutionarily-informed, cognitively-grounded approach to culture, and then apply this approach to explain patterns of food taboos for pregnant and lactating women on Yasawa Island, Fiji. Within a broader cognitive framework, I focus on (1) understanding our capacities for cultural learning as evolved cognitive mechanisms for acquiring adaptive information from other individuals, in a complex, noisy, and changing world, and (2) examining how and when these learning mechanisms result in cumulative cultural evolutionary processes that produce population-level patterns of adaptation and maladaptation. Then, applying this framework, I will argue that the patterns of food taboos observed across three villages in Fiji represent a culturally-evolved adaptation, influenced by various cognitive biases, that protects women, fetuses, and infants from dangerous marine toxins. Our findings indicate that these patterns likely emerged, and are now maintained, by the operation of the cultural learning mechanisms predicted by our evolutionary approach to cognition.

Roberto Delgado - Revisiting Island Differences in Orangutan Socioecology: Behavioral Flexibility and Geographic Variation
2009-03-30 00:00
Roberto Delgado: USC Department of AnthropologyInitial field observations and reports from a few short-term studies pointed to island differences between Bornean and Sumatran orangutans in their general appearance and behavioral ecology, implying meaningful taxonomic distinctions. However, upon further scrutiny at multiple sites and for longer periods of study, researchers have found population-specific differences across a wide array of features including dietary breadth, foraging strategies, life history parameters, molecular markers, morphological characters, reproductive tactics, sociality, tool-using abilities, vocalizations and other traits. Furthermore, the nature of this variation is not always in line with expectations based on a simple island (i.e. Borneo vs. Sumatra) dichotomy, making suspect previous assumptions about historical divergence patterns. Herewith, I review the extent of qualitative and quantitative differences documented and explore a theoretical framework for examining geographic variation and behavioral flexibility among orangutan populations. In particular, I address hypotheses invoking genetic differences, anatomical differences, ecological factors and opportunities for social learning to explain population-level differences. The available data to date suggest that differences in habitat productivity with its concomitant effects on demographic factors such as local population density can influence patterns of gregariousness as well as both the frequency and intensity of social learning within orangutan communities. By examining the occurrence and distribution of geographically varying characteristics such as subsistence skills, comfort skills, and signals, we can determine whether or not the observed patterns of variation are justified with a cultural interpretation when other (i.e. ecological, genetic) explanations are not adequate. Hence, identifying the underlying factors leading to geographic variation in behavior has implications for understanding the emergence of local traditions among great apes as well as the origins and evolution of culture within the human lineage.

Rebecca Bliege Bird - Why Women Hunt: Risk and Contemporary Foraging in a Western Desert Aboriginal Community
2009-03-09 00:00
Rebecca Bliege Bird: Stanford University Department of AnthropologyAnthropologists commonly invoke an “economy of scale” to explain gender differences in hunter-gatherer subsistence and economic production: wives pursue childcare-compatible tasks and husbands, of necessity, provision wives and offspring with hunted meat. This theory explains little about the division of labor among the Australian Martu, where women hunt extensively, and gendered asymmetry in foraging decisions is linked to men’s and women’s different social strategies. Women cooperate with other women primarily hunt small, predictable game (lizards) to provision small kin networks, to feed children, and to maintain their cooperative relationships with other women. They trade off large harvests against greater certainty. Men tend to hunt as a political strategy, using a form of “competitive magnanimity” to rise in the ritual hierarchy and demonstrate their capacity to keep sacred knowledge. Resources that can provision the most others with the most meat best fit this strategy, resulting in an emphasis on kangaroo. They trade off reliable consumption benefits to the nuclear family for more unpredictable benefits in social standing. Among the Martu, gender differences in the costs and benefits of engaging in competitive magnanimity, rather than an economy of scale, structure men’s more risk-prone and women’s more risk-averse foraging decisions. These results suggest an alternative model of the foraging division of labor that emphasizes the role of ecological variance and social competition and de-emphasizes essentialized sexual and reproductive dichotomies.

Patricia Gowaty - It's About Time: Reproductive Decisions Under Ecological and Fitness Constraints
2009-03-02 00:00
Patricia Gowaty: UCLA Department of Ecology and Evolutionary BehaviorDo genes for choosy females and indiscriminate mates determine typical sex roles; or, do ecological and social constraints determine sex roles? Or is sex role determination due to more complex interactions of sex-associated genes and ecological conditions? Answering this question has been difficult, largely because until now there has been no null theory of ecological constraints on sex-associated “sex role” behavior. Here we describe the switchpoint theorem (SPT) that analytically solves the problem of what fraction of potential mates in a population a focal individual of either sex should find acceptable to mate in order to maximize relative lifetime fitness; the SPT is a null model of ecological constraints on reproductive decision-making. The SPT assumes that demographic stochasticity affects time available for mating and that there is variation in fitness that would be conferred by mating with alternative potential mates, to prove that environmental induction of flexible, reproductive decision-making of individuals of both sexes is adaptive. The SPT provides a reasonable scenario for the assumption that all individuals assess likely fitness outcomes before accepting or rejecting a potential mate. Rather than assuming sex differences in genes for choosy females and indiscriminate males, the SPT is a sex-neutral hypothesis that begins with individual differences in ecological constraints to predict induced and adaptive sex role variation. The predictions of the SPT depend on five parameters: individual survival and encounter probabilities, population size, the distribution of fitness that would be conferred by mating with alternative potential mates, and individual latencies (time outs after copulation). The SPT predicts that all else equal, higher probabilities of individual survival and encounters, higher population sizes, and longer latencies decrease the fraction of acceptable mates for focal individuals, so that focal individuals reject more potential mates. Similarly, it predicts that when instantaneous survival and encounter probabilities decline, adaptively flexible individuals accept more potential mates. The SPT provides a novel, quantitative, unified framework for studying how sexual selection and sexual conflict may operate when individuals manipulate the time available for mating of potential mates, their mates, and rivals.

Daniel Nettle - Why is the Theory of Evolution So Hard to Understand?
2009-02-23 00:00
Daniel Nettle: Newcastle University Centre for Behaviour and EvolutionEven in the most developed countries, many people do not accept the theory of evolution as true. Whilst there are cultural and ideological reasons for this, part of the issue is that evolutionary ideas appear to violate certain intuitive beliefs. Even more interestingly, recent research has shown that students who do accept evolution quite systematically misunderstand how it works, tending to endorse species selectionism, the idea that species are born and die abruptly, and models of heredity in which useful characteristics are acquired by all members of the species, not just the progeny of the individuals in which they arise. I will argue that all of these errors arise because in our intuitive cognition about animals, there is little distinction between the species and the individual. Indeed, species are seen as a kind of individual, and individual animals are seen as appearances of the underlying species. This leads people into what Ernst Mayr called typological, rather than population, thinking. I report results of a recent study of conceptualisation of evolutionary change amongst undergraduate students, and argue that a good way of conveying evolutionary ideas is by using human examples, since our intuitive cognition about humans primarily works at the level of individuals, their family relationships, and the ways they are different from other members of their species.

David Sloan Wilson - Evolving the City: Using Evolutionary Theory to Understand and Improve the Quality of Everyday Life
2009-02-17 00:00
David Sloan Wilson: SUNY Binghamton Department of Biological
Sciences & Department of AnthropologyEvolutionary theory is rapidly expanding beyond the biological sciences to include all human-related subjects in academia. Since evolution is fundamentally about organisms in relation to their environment, basic scientific research needs to focus on people from all walks of life, as they go about their daily lives. This kind of research is also most relevant for improving the quality of everyday life, leading to a positive tradeoff between basic and applied science. I will provide an overview of The Binghamton Neighborhood Project, a unique “whole university/whole city” approach to community-based research from an evolutionary perspective.

Robert Boyd - The Evolution of Social Stratification
2009-02-09 00:00
Robert Boyd: UCLA Department of AnthropologyIn this talk I explain how culturally heritable differences in wealth between social groups can arise and be maintained even when the only adaptive learning process driving cultural evolution increases individuals’ economic gains. The key assumptions are that human populations are structured into groups and that cultural learning is more likely to occur within groups than between groups. Then, if groups are sufficiently isolated and there are potential gains from specialization and exchange, stable stratification can sometimes result. This model predicts that stratification is favored by (1) greater surplus production, (2) more equitable divisions of the surplus among specialists, (3) greater cultural isolation among subpopulations within a society, and (4) more weight given to economic success by cultural learners. I will conclude by arguing that this mechanism may explain why there is much more heritable variation among groups within the human species than in other taxa.http://www.sscnet.ucla.edu/anthro/faculty/boyd/HenrichBoydCA0908.pdf

Nathan Bailey - Same-sex Mating Behavior and Evolution
2009-02-02 00:00
Nathan Bailey: UC Riverside Department of BiologySame-sex mating behavior has been extensively documented in non-human animals, but we still know relatively little about its evolutionary impact. What evidence exists that same-sex sexual behavior can be adaptive? Do the genetic and physiological mechanisms underlying same-sex mating help explain its ultimate cause and maintenance in populations? How flexible is it, and what is the significance of that plasticity? And can same-sex mating interactions influence the evolutionary dynamics of populations? My talk will draw upon studies published in the last several years in a wide variety of non-human animals to highlight discoveries addressing the role of same-sex sexual behaviors as agents of evolutionary change. I will focus on both the evolutionary causes and consequences of same-sex mating behavior. However, the bulk of the discussion will be organized around the second theme, because recent studies suggest that the impact of same-sex mating behavior on population-level processes can be powerful and of considerable importance.

James Fowler - Genes and Social Networks
2009-01-26 00:00
James Fowler: UCSD Political Science DepartmentSocial networks exhibit strikingly systematic patterns across a wide range of human contexts. While genetic variation accounts for a significant portion of the variation in many complex social behaviors, the heritability of egocentric social network attributes is unknown. Here we show that three of these attributes (in-degree, transitivity, and centrality) are heritable. We then develop a “mirror network” method to test extant network models and show that none accounts for observed genetic variation in human social networks. We propose an alternative “Attract and Introduce” model with two simple forms of heterogeneity that generates significant heritability as well as other important network features. We show that the model is well suited to real social networks in humans. These results suggest that natural selection may have played a role in the evolution of social networks. They also suggest that modeling intrinsic variation in network attributes may be important for understanding the way genes affect human behaviors and the way these behaviors spread from person to person.http://arxiv.org/abs/0807.3089

Karthik Panchanathan - Quantifying the Bystander Effect in a Multi-Player Dictator Game
2009-01-12 00:00
Karthik Panchanathan: UCLA Department of AnthropologyBehavioral economics studies have shown people to have other-regarding social preferences. In the Dictator Game, for example, dictators transfer some portion of their endowment to recipients, who start out without an endowment. If people were self-interested, those assigned the role of dictator would keep all of their endowment; those assigned to be recipients would go home with nothing. In social psychology, scores of studies document the Bystander Effect, in which the likelihood of receiving help declines as the number of potential helpers increases. To reconcile pro-social preferences with the Bystander Effect, psychologists propose the notion of diffusion of responsibility: while people want to see the victim helped, they feel less of a responsibility to help when others are present and able to help. Here, we present results from two multi-player dictator games, one in the lab with real stakes (N=196) and one online with hypothetical stakes (N=215), to look for evidence of the diffusion of responsibility in an experimental economics setting.

Caleb Finch - The Role of Diet and Infection in Human Evolution
2009-01-05 00:00
Caleb Finch: USC Davis School of GerontologyHuman lifespans have increased remarkably from the 20 year life expectancy (LE) of the great apes. The normative 40 y LE of pre-industrial peoples has recently risen to about 80 y in privileged populations during the last 200 years. I propose that diet and infections are key to understanding both demographic transitions. During human evolution, human ancestors shifted from a largely plant based diet to include larger amounts of animal tissues and cholesterol intake that observed in the extant great apes. Exposure to infections also increased because of consumption of raw tissues and from close contact with feces not observed in great apes which rarely use the same night nest. In 2004, Craig Stanford and I hypothesized that “meat-adaptive genes” enabled these transitions (Q Rev Biol. vol 79, 2004). Apolipoprotein E is a candidate for pleiotropic genes with influences on blood lipids, innate immunity, and brain development; the apoE3 allele that increases LE spread in human populations about 225,000 years ago. I will further discuss the possible role of apoE alleles and other genes in supporting the recent increase in LE during post 18th century improvements of diet and reduction of infections.

Peter DeScioli - The Alliance Hypothesis for Human Friendship
2008-12-01 00:00
Peter DeScioli: Chapman University, Economic Science InstituteExploration of the cognitive systems underlying human friendship will be advanced by identifying the biological functions these systems perform. Here I propose that human friendship results from cognitive mechanisms designed to assemble support groups for potential conflicts. I draw on game theory to identify computations about friends that can increase performance in multi-agent conflicts. This analysis suggests that people would benefit from: 1) ranking friends, 2) hiding their friend-ranking, and 3) ranking friends according to their own position in partners’ rankings. These possible tactics motivate the hypotheses that people possess egocentric and allocentric representations of the social world, that people are motivated to conceal this information, and that egocentric friend-ranking is determined by allocentric representations of partners’ friend-rankings (more than others’ traits). I report several investigations designed to test predictions derived from these hypotheses. The results suggest that the alliance hypothesis merits further attention as a candidate explanation for human friendship.

Tatsuya Kameda - Emotional Functioning and Socio-Economic Uncertainty: Is "Hikikomori" an Indigenous Cultural Pathology in Japan?
2008-11-24 00:00
Tatsuya Kameda: Hokkaido University Department of Behavioral ScienceFeeling and expressing emotions appropriately in the right context is an essential component of social behavior. It has been suggested that emotional functioning has been weakened among contemporary Japanese youth, who exhibit acute social withdrawal, a “cultural pathology” known as Hikikomori (Hattori, 2005; Zielenziger, 2006). Assuming that Hikikomori is at least partially caused by socio-economic uncertainties faced by younger generations, we predicted that the syndrome is not confined to a clinical subpopulation but should be manifested by even undiagnosed youth, though in moderated form, as a negative function of their family socio-economic status (SES). Results from an emotion-sampling study â€“ in which participants’ reported their momentary emotional states 12 times per day for one-week during the course of their daily lives â€“ and a laboratory experiment â€“ which measured psycho-physiological responses to emotional stimuli â€“ both supported this prediction. Implications of these findings for the well-being of youth in well-developed, post-industrial societies are discussed.

John Mikhail - Universal Moral Grammar: Theory, Evidence, and Future Research
2008-11-17 00:00
John Mikhail: Georgetown LawScientists from various disciplines have begun to focus renewed attention on the psychology and biology of human morality. One research program that has recently gained attention is universal moral grammar (UMG). UMG seeks to describe the nature and origin of moral knowledge by using concepts and models similar to those used in Chomskyâ€™s program in linguistics. This approach is thought to provide a fruitful perspective from which to investigate moral competence from computational, ontogenetic, behavioral, physiological, and phylogenetic perspectives. In my talk, I first outline a framework for UMG and describe some of the evidence supporting it. I then discuss some initial findings of a related study in comparative law that seeks to determine how certain norms, such as the prohibition of homicide, are codified and interpreted in several hundred jurisdictions around the world. The studyâ€™s main finding, the apparent universality or near-universality of specific justifications and excuses, lends further support to UMG. It also raises novel questions for cognitive science, broadly construed, including neuroethics, behavioral economics, evolutionary psychology, and legal anthropology.http://papers.ssrn.com/abstract=1163422

Noah Goldstein - The Constructive, Destructive, and Reconstructive Power of Social Norms
2008-11-10 00:00
Noah Goldstein: UCLA Anderson School of ManagementSocial norms can be powerful drivers of human behavior, which means that communicators who can properly harness norms hold in their hands a powerful tool for persuasion. If utilized properly, communicators can effectively convey such norms in ways that motivate individuals to engage in positive, constructive behaviors that benefit not only those individuals themselves but society as a whole. However, even thoughtful and well meaning communicators can convey norms ineffectivelyâ€”or worse, elicit a negative, destructive backfire effect that may exacerbate an already unappealing situation. Yet, even in such instances, when a certain social norm leads individuals to perform destructive behaviors, other types of social norms can be employed to mitigate the negative influence of that norm. I will discuss how, when, and why different kinds of social norms play constructive, destructive, and even reconstructive roles in motivating human behavior.
