Center for Behavior, Evolution, and Culture

Eduardo Fernandez-Duque - The Importance of Food, Jealousy, and Paternal Care in the Evolution of Owl Monkey Monogamy
2015-03-04 00:00 (America/Los_Angeles)
Eduardo Fernandez-Duque: Yale UniversityI will discuss published and new data from a population of monogamous owl monkeys in the Argentinean Chaco that we have been studying for almost 20 years to examine the hypothesis that social monogamy is a default social system imposed upon males because the spatial and/or temporal distribution of resources and females makes it difficult for a single male to defend access to more than one mate. Over the years we have tested predictions on ranging patterns, use of space, population density and the abundance and distribution of food. We have also examined the extent to which the ranging and ecological data allow us to predict demographic and life-history parameters as proxies for reproductive success.

John Tooby - Political Epidemiology, History, and the Evolutionary Psychology of Outrage.
2015-03-09 00:00
John Tooby: UCSBDon’t shoot! Rodney King. Remember the Maine. The Reichstag Fire. Guernica. The War of Jenkins Ear. The murder of Emmet Till. Events in which one or more members of one group injure the welfare of one or more members of another group (“outrages”) typically provoke extraordinarily strong and frequently violent responses directed more or less indiscriminately at members of the group from which the offender or offenders came. Such events are treated entirely differently than parallel harms performed by individuals within groups. They unleash cultural processes in which accounts of harms rapidly spread through the group the victims came from. Generally, as news of the (sometimes fabricated) harm is transmitted from person to person, details are added to representations of the event so that the actions depicted seem harsher, more intentional, and more group-targeted. Many group members treat inflammatory portrayals of interactions and the rage they generate as a kind of precious group resource, becoming very resistant to contrary evidence, and passing these stylized narratives down generations. News of outrages strongly motivate the desire to join with others to act in a coordinated and aggressive fashion “against” the other group. A review of the historical and ethnographic record suggests that outrages play a central role in starting wars, provoking ethnic violence, and in mobilizing social movements and revolutions. The cross-culturally and cross-historically recurrent structure of these cultural and social phenomena can be understood by seeing how they naturally emerge from interactions between the evolved psychology of welfare tradeoffs, groups, adaptations for group coordination, and common knowledge. The key is that cross-group harms, if uncontested, are implicitly seen as proposing a common knowledge precedent for the degree of social domination or subordination. The psychology of outrages can be seen as a parallel and complementary adaptation to leadership—one way of solving the coordination problem of mobilizing group members to effectively act or bargain in conflicts with outgroups. Because it is normally difficult to get individuals to set aside competing agendas within groups, yet group power increases with coordination, outrages (real or fabricated) become a resource ingroup individuals strategically deploy to mobilize joint action they (as individuals) expect to benefit from.

Robert Provine - From Laughter to Speech Evolution: A Bipedal Perspective
2015-03-30 00:00
Robert Provine: University of MarylandAfter an introduction to the nature and use of laughter in daily life, discussion turns to the
evolution of laughter and its implications for the emergence of speech.
Contrasts between human and chimpanzee laughter reveal that laughter is the ritualized
signal of labored breathing of rough-and-tumble, with the vocalization representing
the playful context of its origin. Laughter is primate onomatopoeia that signals, “this
is play, I’m not attacking you.” The ancestral primate laugh as performed by extant
chimpanzees is a noisy, unvoiced “pant-pant” in which one vocalization is uttered per
inward and outward breath. Naïve human observers do not recognize this utterance as
laughter, volunteering that it sounds like panting, perhaps of a dog, or even sawing or
sanding. In contrast, humans laugh as they speak, by modulating (parsing) an exhalation
into voiced bursts of “ha-ha.” Chimpanzee laughter suggests why they cannot speak–
they are confined to one utterance per inward and outward breath. The breakthrough in
human respiratory control necessary for speech came with evolution of bipedal running.
Chimpanzees and other quadrupeds have a 1:1 ratio between stride and respiratory cycle,
a necessary adaptation for forelimb impacts during running. (Without inflated lungs,
the thorax is a floppy, air-filled bag.) An unappreciated consequence of the evolution
of bipedal human locomotion is the freeing the thorax of its support function during
running, and the associated uncoupling of respiration and locomotion. Unlike the 1:1
strides per breath ratio of quadrupeds, humans runners have highly variable ratios of
4:1, 3:1, 5:2, 2:1, 3:2, or 1:1, with 2:1 being most common. With the uncoupling of
respiration and locomotion during bipedal running, there is more voluntary control of
breathing and greater opportunity for the natural selection for longer and more complex
vocalizations, including human laughter and speech. This is the bipedal theory of speech
evolution.

No BEC This Week -
2015-04-06 00:00
No BEC This Week:

Meg Crofoot - Collective Decision-Making in Complex Societies: Lessons From Tracking Wild Baboons
2015-04-13 00:00
Meg Crofoot: UC DavisAnimals living in stable social groups may often disagree about where to go, but must reconcile their
differences to maintain cohesion and thus the benefits of group living. Although theory predicts that
shared (democratic) decision-making should be widespread in nature, in species that form long-term
social bonds, considerable asymmetries in dominance and social power often exist, and some have
proposed that these differences give high-ranking individuals increased influence over group decisions.
Determining how consensus is achieved in stratified societies remains a core challenge for
understanding the evolution of social complexity. To investigate how differentiated social relationships
shape the collective decision-making process, we captured simultaneous high-resolution GPS tracks
from 26 members of a wild olive baboon troop (Papio anubis; ~ 80% of adult and subadult members,
sampled at 1hz). We then used these data to explore the relative importance of individual relationships
vs. majority rule in driving group movement decisions in this highly structured society.

Rick Dale - Adaptiveness of Language: From Real-Time Processes to Linguistic Typology
2015-04-20 00:00
Rick Dale: UC MercedHuman language is a flexible behavioral repertoire that may be finely tuned to our cognitive processes and social circumstances. I present evidence from three timescales that language may be shaped by a number of social and cognitive variables. These timescales include (i) how language is used in real-time human interaction, (ii) how language use may relate to the structure of social groups, and (iii) how slower-changing aspects of language, such as grammatical structure, may relate to large-scale demographic variables. I will then examine whether these relationships at different timescales provide hints of selection processes operating over language, and end with a new study demonstrating that, indeed, we can detect “echoes of selection” in large-scale vocabulary data.

Emma Cohen - Social Bonding in Movement and Exercise
2015-04-27 00:00
Emma Cohen: University of OxfordIn this talk, I’ll present some ideas and preliminary data on the links between exercise and social bonding. Exercise, broadly construed, is a cultural universal – from ceremonial rituals to team sports, people everywhere get together to move together. Our research investigates whether and how such activities serve a social bonding function, as has been long claimed in the social scientific literature. Specifically, we explore the social bonding effects of behavioural coordination and exercise ‘highs’. We are also interested in the effects of social bonding on exercise ability and performance, particularly on pain perception and fatigue thresholds. The research attempts to reveal mechanisms underlying the links between coordinated movement, pleasure and pain, and bonding and wellbeing and thereby to contribute new data on a pervasive feature of everyday life that cross-cuts cultural domains as varied as religion, sport and play.

Lera Boroditsky - How the Languages We Speak Shape the Ways We Think
2015-05-04 00:00
Lera Boroditsky: UCSDHow do the languages we speak shape the ways we think? Do speakers of different languages think differently? Does learning new languages change the way you think? Do bilinguals think differently when speaking different languages? Does language shape our thinking only when we’re speaking or does it shape our attentional and cognitive patterns more broadly? In this talk, I will describe several lines of research looking at cross-linguistic differences in thought.

Laurie Santos - The Evolution of Irrationality: Insights from Non-Human Primates.
2015-05-11 00:00
Laurie Santos: Yale UniversityI will explore the evolutionary roots of some of our species’ irrational decisions. I will start by reviewing some classic biases in the field of judgment and decision-making and will then turn to the question of how these biases came about in the first place by exploring some recent experiments in exploring similar biases in monkeys. I will then discuss new work suggesting ways that the human species is uniquely irrational.

Jacob Foster - The Unknown Known: Science, Social Learning, and Cultural Evolution
2015-05-18 00:00
Jacob Foster: UCLAScience is an incredibly successful instance of social learning. Its practices produce and subtly organize the attention, effort, and creativity of millions of scientists, leading to rapid and cumulative cultural evolution. In this talk, I outline the striking convergence between this view of science and the one developed in science studies. Using data from millions of scientific papers, I illustrate how scientists use social cues to select research problems and how these heuristics lead to more (and less) efficient discovery. I then argue that formal theories of learning and cultural evolution shine new light on old puzzles in the sociology of science–while the study of science provides provocative problems, parallels, and paradigms for theories of cultural evolution.

A.J. Figueredo and Michael Anthony Woodley - A Sequential Canonical Cascade Model of Social and Cognitive Biogeography
2015-06-01 00:00
A.J. Figueredo and Michael Anthony Woodley: University of Arizona, Free University of BrusselsA sequential canonical cascade model, detailing the hypothesized biogeography of human life history (LH) and intelligence (IQ), derives elevated levels of IQ through a series of causal steps, starting with the evolution of slower LH strategies based on both the physical ecology (climatological factors) and community ecology (population density and parasite burden). This model then examines the social ecology of slow LH strategy through the establishment of cooperative and mutualistic social systems with enhanced levels of social equality, within-group and between-group peace, and sexual equality. These social sequelae, in turn, lead to the strategic differentiation of resource allocation profiles among slower LH strategists (the SD-IE effect) that foster socioecological niche-splitting through intraspecific character displacement and produce mutual competitive release among individuals in saturated, resource-limited environments. By producing cooperative systems of specialists that each efficiently exploit different social micro-niches, the mutual exchange of resources so derived inevitably triggers the action of Ricardo’s Law of Comparative Advantage, producing greater aggregate wealth through these emergent social properties than would otherwise be attainable to equal numbers of generalists. We track this hypothesized mediating mechanism through the relations among three major macroeconomic indicators at the national level of aggregation: higher Economic Complexity Indices, lower Gross Domestic Product Dissimilarity Indices, and lower Krugman Dissimilarity Indices. Finally, we explain how this combination of powerful macroeconomic forces inevitably produces massive increases in aggregate wealth that elevate the collective human capital of the entire society, enhances physical brain volume, and contributes to higher overall levels of human cognitive abilities.

Kristin Snopkowski - Reproductive Decision-Making in Transitional Contexts
2015-09-28 00:00
Kristin Snopkowski: Boise State UniversityOver the past two hundred years, most societies around the world have experienced fertility transitions, defined as a dramatic decline in reproductive rates through time. The conscious decision to reduce fertility to very low levels appears maladaptive and poses a theoretical challenge to human behavioral ecologists who expect humans to maximize long term fitness. I develop a theoretical model to explain currently low fertility rates that incorporates both cultural and economic hypotheses of fertility decline and test these using data from San Borja, Bolivia, a society currently undergoing a fertility transition. Results show that both economic and cultural information are important determinants of reproductive decisions. Kin are also an important influence on reproductive decision-making, possibly providing help to a reproducing couple or hindering reproduction by engaging in resource competition. I test these hypotheses using data from Thailand and Indonesia and show that couples who receive help from kin are more likely to reproduce in the future, providing evidence for the cooperative breeding hypothesis. Finally, I present some preliminary results from my recent field season in Huatasani, Peru exploring men’s reproductive decision making and discuss theoretical models of sexual conflicts over family size.http://www.sscnet.ucla.edu/anthro/snopkowski-bec-talk.pdf

Dan Franks - The Evolution of a Long Post-Reproductive Lifespan in Killer Whales
2015-10-05 00:00
Dan Franks: University of YorkWhy females of some species cease ovulation before the end of their natural lifespan is a longstanding evolutionary puzzle. In humans as well as some natural populations of cetaceans and insects, reproductive aging occurs much faster than somatic aging and females exhibit prolonged post-reproductive lifespans (PRLSs). Determining the mechanisms and functions that underpin PRLSs has proved a significant challenge. Here we bring together both classic and modern hypotheses proposed to explain PRLSs and discuss their application with particular reference to our studies of killer whales. In doing so we highlight the need to consider multiple interacting explanations for the evolution of PRLSs.

Erik Gjesfjeld - Social and Technological Responses to Risk and Uncertainty: A Material Culture Approach
2015-10-12 00:00
Erik Gjesfjeld: UCLAIn both the past and present, human populations are consistently presented with unpredictable situations. Behavioral responses to these situations are often heavily mediated by our degree of knowledge (uncertainty) about the variability in outcomes (risk). Using social network analysis as well as a novel macro-evolutionary method for examining the mode and tempo of evolution, this research explores changes in material culture diversity in response to increased environmental and economic risk. Results from this research suggest that social networks can be an important mechanism for reducing hunter-gatherer uncertainty surrounding environmental fluctuations, but technological innovations do not tend to buffer economic risk, as is commonly thought. Overall, these findings help to highlight some of the misconceptions surrounding risk and support the continued analysis of risk-sensitive adaptations using material culture.

Tim Shields - The Demonstrability of What You Have Not Done (But Could Have) Matters In Trust-based Exchange
2015-10-19 00:00
Tim Shields: Chapman UniversityWe describe results of a study in trust-based exchange that supports the proposition that humans perceive intention not only through what others do but also through what others choose not to do. Crucial to this proposition is the notion that trust-based exchanges entail decision dilemmas where mutually exclusive goals are traded off and the forgone opportunities produce clues about our intent – affecting others’ reactions. To manipulate the availability of foregone opportunities, we used two versions of the trust game in a 1×2 between subjects design. In two experimental trust games, the action space governing trustors’ transfers was manipulated to examine the effects on trustors’ transfers and trustees’ returns. In the “all-or-nothing” game the trustor could transfer either $10 (all) or $0 (nothing), while in the “continuous” game the trustor could transfer any amount between $10 and $0. In both games, the trustee received the tripled transfer and then could return any amount (to trustor). Trustors transferred significantly more in the all-or-nothing game than in the continuous game. However, higher initial transfers in the all-or-nothing game did not lead to larger returns. To the contrary, conditional on $10 transfers, on average trustees returned significantly less in the all-or-nothing game than in the continuous game. Although the all-or-nothing action space results in greater wealth overall, trustors do not benefit from this increased wealth. These results suggest that the availability of alternative options is paramount in shaping social behaviors.

Debra Martin - CANCELLED -- Ancient Bones, Ancestral Bodies: Interpretive Approaches to Violence and Behavior
2015-10-26 00:00
Debra Martin: University of Nevada, Las VegasViolence (lethal and nonlethal) is often associated with social spheres of influence and power connected to daily life such as subsistence intensification, specialization, resources, climate, population density, territorial protection and presence of immigrants, to name just a few. By using fine-grained biocultural analyses that interrogate trauma data in particular places at particular times in reconstructed archaeological contexts, a more comprehensive view into the behaviors, histories and experiences of violence emerges. Moreover, identifying culturally-specific patterns related to age, sex, and social status provide an increasingly complex picture of early small-scale groups. Some forms of ritual violence have restorative and regenerative aspects that strengthen community identity. Other forms of social violence cause rupture and disintegration at the group level. Bioarchaeological data can shed light on the ways that violence becomes part of a given cultural landscape. Viewed in a biocultural context, evidence of osteological trauma provides rich insights into social relationships and the many ways that violence is embedded within those relationships.

Drew Rendall - Language Evolution and The (Ir)relevance of Primate Communication
2015-11-02 00:00
Drew Rendall: University of LethbridgeThe evolution of language is a longstanding problem that continues to invite study, analysis, and speculation from a variety of perspectives. One perspective has been to adopt a comparative stance and seek the rudiments of key elements of language in the communication systems of closely related nonhuman primates. While sensible enough, in principle, I’ll argue that this search has been focused in the wrong places (like the drunk fumbling in the dark searching the ground for his keys, not where they’re most likely to be but rather simply where the light is brightest) namely on high-level informational properties of language related to its intentionality, semantics and syntax. Several decades of such focused research now points to the conclusion that, in these respects, primate communication is largely irrelevant. So, despite their phylogenetic proximity to us, are other primates in fact not really relevant to the problem of language evolution? I’ll answer, no… and promise to disambiguate that answer. In the process, I’ll hope to make some broader points about the enterprise of theorizing, both in this field but also more generally, considering how the constructs we use, the explanatory metaphors we borrow, and (ironically?) the language we adopt can steer the phenomena we study and aim to explain, as much as the reverse, potentially leading us to mistake purely theoretical entities for real ones.

Elly Power - Signaling, Status, and Social Networks: Religious Practice in Rural South India
2015-11-09 00:00
Elly Power: Santa Fe InstituteDiscerning the intentions and character of others is a difficult task. In South India, religious practice is seen as particularly helpful in that process of discernment. There, the ritual acts undertaken are often quite dramatic: devotees walk across hot coals, pierce their skin with hooks and spears, walk barefoot to distant temples, and sacrifice animals to the divine. What is being communicated through these acts? Drawing on reputational and social support network data, I show that greater and costlier ritual participation corresponds to greater recognition not only for being devout, but also for holding a suite of prosocial traits. Perhaps more importantly, greater and costlier ritual participation also increases the likelihood of a supportive tie between individuals. These findings provide clear support for the costly signaling theory of religion. However, I will spend much of the talk complicating these simple relationships. Not everyone performs costly ritual acts, and the reputational benefits that accrue to those who do are not equally distributed. Much of this variation can be explained by the social risks entailed in these acts and the differential ability of villagers to take on those potential costs. To fully understand this signaling system, a broader understanding of cost, a wider range of actors, and a more complete inventory of signals (including not only the dramatic but also the subtle) must all be recognized and taken into account.

Joey Cheng - Getting to the Top: Pathways to Social Rank
2015-11-16 00:00
Joey Cheng: University of Illinois at Urbana-ChampaignThe pursuit of social rank is a recurrent and pervasive challenge faced by individuals across human societies. Yet, the precise means through which individuals compete for social standing remain unclear. This talk examines the dynamics of two fundamental avenues—fear and respect—to social rank. I will begin by highlighting how these strategies differ—in terms of their characteristic personality, emotional, verbal, and nonverbal patterns. I will then present evidence demonstrating the viability of fear and respect for effectively ascending the social hierarchy in both the lab and the field. Finally, I will discuss new research that examines the impact of fear- and respect-based leadership on group functioning and follower well-being. Taken together, this emerging line of research suggests that fear and respect represent two distinct pathways to social rank. Underpinned by a unique suite of cognitive, affective, and behavioral processes, these pathways shape the hierarchical order of individuals within groups and promote collective success, albeit under different circumstances.

Melissa Emery Thompson - On Less Fertile Ground: Chimpanzee Life Histories in Context
2015-11-23 00:00
Melissa Emery Thompson: University of New MexicoAmong the most dramatic changes to occur during human evolution were those affecting our life history. The evolution of the human fertility pattern, including relatively fast birth rates, overlapping offspring dependencies, and extended postreproductive life, remains an active area of research and debate that can be greatly informed by structured comparisons to the living apes. To do so effectively, we need high quality data from natural populations, as well as more detailed information about the physiological mechanisms that regulate fertility in both species. To that end, I will discuss empirical data on reproductive lifespan, determinants of fecundity, regulation of the interbirth interval, and parental investment in wild chimpanzees with comparison to human populations. Humans and chimpanzees share remarkably similar patterns for the regulation of fertility. Despite the relatively higher cost of human infants, human mothers appear less constrained by their reproductive systems than are chimpanzee mothers. These data support the view that the social context of reproduction has been a fundamental contributor to changes in life history.

Elizabeth Cashdan - Sex Differences in Mobility and Wayfinding: Cross-Cultural Perspectives
2015-11-30 00:00
Elizabeth Cashdan: University of UtahSex differences in range size and navigation are widely reported, with males traveling farther than females, being less spatially anxious, and, in many studies, navigating more effectively. We want to know why males range farther, and what this might tell us about sex differences in wayfinding and spatial confidence. Proposed evolutionary explanations have suggested that males gain mating benefits from large ranges (mating hypothesis), while females incur greater fitness costs from such travel due to parenting constraints (parenting hypothesis). We find support for both hypotheses, but a comparison of the polygynous Twe and the monogamous Maya suggests that the importance of the two hypotheses varies facultatively with mating patterns. Our work in Utah also indicates that women’s greater harm avoidance is a partial mediator of the sex difference in mobility, which in turn affects navigational style and ability.

Brenna Henn - Answering Major Questions in Modern Human Origins with Genome Data
2016-01-04 00:00
Brenna Henn: SUNY Stony BrookOver twenty-five years ago, geneticists sequenced mitochondrial DNA from a diverse sample of human populations and hypothesized that all humans have a common origin in Africa 200,000 years ago.The broad outlines of this hypothesis remain remarkably unaltered, but many details of our African origin continue to be elusive. After decades of advances in human genetics, we are no longer data limited (either in terms of samples or genomic loci) but there is little consensus on most key issues. I will outline the models underlying the origin of modern humans. For example, was there a single ancestral population or multiple ancestral populations? Additionally, is there a discordance between anatomically modern humans and behaviorally modern humans? I will explore patterns of genetic diversity across Africa, the complex history of southern African KhoeSan groups and adaptations to African environments. I discuss whether genetic data supports archaeological data and suggest directions for future research.

Bruce Ellis - Childhood Experience, Development of Reproductive Strategies, and Health: An Integrative, Life History Framework
2016-01-11 00:00
Bruce Ellis: University of ArizonaLife history theory is used to explain how individuals adapt their physiology, behavior, and reproduction to different social and ecological conditions. Using a life history framework, I will present a program of research examining linkages between childhood experiences (including familial and extra-familial conditions), pubertal development, sexual activity, and health, highlighting the important distinction between harsh versus unpredictable environmental contexts, the special role of fathers in regulating daughters’ sexual development, differential susceptibility to environmental influences, and effects of life-history trade-offs on health. An evolutionary, life history perspective emphasizes that, when organisms encounter stressful environments, it does not so much disturb their development as direct or regulate it toward strategies that are adaptive under stressful conditions, even if those strategies are currently harmful in terms of the long-term welfare of the individual or society as a whole.

Marcus Hamilton - Biological Scaling and the Evolution of Human Ecology
2016-01-25 00:00
Marcus Hamilton: Santa Fe InstituteWe can observe, examine and study the world around us meaningfully at many scales. Biologists may study genes, populations, species, ecosystems, or the biosphere. Social scientists may study the behavior of individuals, the dynamics of cities, or aspects of the archaeological past. But of course, at a coarse-grained level we are all examining the same system, just at different scales, and so the question then becomes; how do we integrate across all these scales to understand something about the fundamental mechanisms driving the complexity of living systems, including humans? In this talk I will introduce the scaling approach to understand the structure and function of biological systems, and how we can leverage insights gained in the biological realm to understand how human ecology has evolved. I will argue that economies of scale are fundamental to life, including human societies, and the scaling approach provides a powerful mathematical and statistical framework for understanding why.

Stephanie White - Cycling in the Brain: Molecular Insights Into Vocal Learning
2016-02-01 00:00
Stephanie White: UCLAHumans and songbirds learn their vocalizations through social interactions and sensorimotor experience. These processes enlist implicit learning, a critical component of social cognition. Deficits in implicit learning including language disorders have devastating consequences for social integration and well-being. To treat or prevent these deficits, the neural mechanisms for learned vocal communication must be understood. Songbirds are one of the few animal models in which one can study the language subcomponent comprised by socially-learned vocal communication because, like humans but unlike rodents or non-human primates, they learn a significant portion of their vocalizations. They do so in a manner that exhibits key parallels to speech development and maintenance. Parallels include reliance on critical periods, cortico-basal ganglia circuitry, ongoing auditory inputs, hormonal factors and genes such as the forkhead transcription factor known as FoxP2. Using behavioral paradigms, we found that songbirds actively regulate their own levels of FoxP2 within area X, the basal ganglia sub-region dedicated to vocal learning. We paired this ethological approach with modern systems analytic techniques and found that singing activates distinct ensembles of gene expression in area X that are not similarly co-activated in adjacent tissue comprised of similar cell types. Thus, ‘molecular microcircuitry’ exists alongside anatomic and synaptic microcircuitry that, together, functionally specify the brain, in this case, for vocal learning. Behavior-linked regulation of this molecular microcircuitry appears critical for vocal learning.

Sean Prall - Immunity, Stress, and Development: The Role of Adrenal Androgens in Human Evolutionary Biology
2016-02-08 00:00
Sean Prall: University of Washington School of MedicineThe developmental pattern of adrenal androgen production is unique to humans and chimpanzees, and this pattern is thought to have important implications in human evolutionary biology. Unlike other hormones, the ultimate role of adrenal androgens is not well understood despite the important physiological roles these hormones play. The adrenal androgen DHEA in particular has been implicated in shaping cognitive evolution, acting in an adaptive fashion to buffer the effects of stress, and as an important agent in bolstering immunocompetence. Recent research in the pattern of development in orangutans suggests adrenal androgen production is shared across higher apes, and is not likely related to primate social conditions. In humans, DHEA is found to play potent and diverse roles in different aspects of immune function, suggesting an important role for human ecoimmunology. Additionally, DHEA is related to acute and chronic stress activation, and may play an adaptive role in shaping acute stress responses. These results shed light on an evolutionary and physiologically relevant hormone, and implicates DHEA as an important mediator of human life history strategies.

Paul Smaldino - Learning About Social Evolution with Extremely Unrealistic Models
2016-02-22 00:00
Paul Smaldino: UC DavisThe lives of social animals, none more so than humans, are shaped by cooperative interactions. Sharing, exchange, and synergy are the name of the game. Understanding the origins of cooperative behavior with any clarity often requires formalization of theories in the way of mathematical and computational models. These models by necessity ignore many details of an organism’s ecology, life history, and behavioral repertoire. Nevertheless, models provide crucial scaffolds for theory development, partly by explicitly declaring all of their assumptions and thereby making their limitations clear. That said, we can always stand to improve. I will discuss mathematical and computational models of the evolution of cooperative behavior, and how our assumptions about individual behavior, life history, and environmental structure influence our conclusions concerning how social populations evolve. In particular, I will focus on the advantages of complicated models in which life history and population structure are included, even when those factors are not the explicit targets of investigation.

Mirta Galesic - Early Development of Human Cooperation: The Role of Interdependence
2016-02-29 00:00
Mirta Galesic: Santa Fe InstituteThe importance and scale of cooperation in human societies is unmatched among other primates and is considered to be a major contributor to our species’ exceptional success. Given that cooperation seems so useful, it is surprising that it flourished only in humans but not in other primates who had similar cognitive abilities as our ancestors or lived in similar circumstances. Large-scale human cooperation is successfully explained by models of cultural group selection, but these models require a relatively advanced social cognition already in place. To explain early origins of human social cognition and cooperation, cooperative breeding and cooperative foraging accounts have been proposed. However, computational models of these accounts that would enable more precise understanding of the underlying mechanisms are still scarce.
We develop a computational model of one possible mechanism underlying the early development of human cooperation, based on interdependence. We show that the interdependence might have increased because several otherwise non-remarkable and ubiquitous factors came together for our early ancestors: specific physical properties of Early Pleistocene environments, characteristics of our early ancestors’ social structure, and their cognitive abilities. Together, these factors might have led to increased value of group foraging, which in turn led to increased interdependence, and eventually to higher propensity to share food with non-kin. This propensity could have been instrumental for the development of further prosocial tendencies, ultimately paving the way for the development of large-scale cooperation through cultural group selection, emerging in Middle and Late Pleistocene.

Jeff Winking - State of the Union: The Fate of the Paternal Investment Model of Human Marriage
2016-03-07 00:00
Jeff Winking: Texas A&MFathering traditionally played a central role in the evolutionary stories of human marriage. Paternal investment proved a convincing lynchpin linking together numerous hallmark aspects of the human adaptive strategy: the capacity for long-term romantic bonds, altricial infancy, extended juvenile dependence, etc. However, recent theoretical work suggests that the importance of paternal investment is an unlikely candidate for the primary selective force behind the evolution of long-term pairing in humans; indeed, paternal care likely evolved within the context of pre-existing pair-bonds. Here I explore the numerous scenarios that have been put forth to explain the “marriage-first” phylogenetic order and the role that paternal investment still plays in reconstructing the evolution of human pair-bonding.

Chris Kuzawa - Brain Energetics and The Evolution of Human Childhood
2016-03-28 00:00
Chris Kuzawa: Northwestern UniversityHumans are unusual in having a childhood stage characterized by a prolonged period of exceptionally slow growth. Many hypotheses have been proposed to explain why humans have evolved this life history stage. In this talk, Chris Kuzawa will discuss his recent collaborative work that quantifies the costs of human brain development and uses this information to shed light on the evolution of human life history. Compiling data from brain imaging studies, they find that the costs of the brain do not peak at birth, when relative brain size is largest, but at 4-5 years of age, when the brain consumes the equivalent of 66% of the body’s energy use at rest. This childhood peak in brain costs reflects the proliferation of energy-intensive synapses prior to experience-driven synaptic pruning. Consistent with the hypothesis of a brain-body growth trade-off, body weight growth rate follows an inverse, linear relationship with brain glucose demands from infancy until puberty, and maximal brain glucose demands co-occur developmentally with the age of slowest body weight gain. These findings provide rare empirical evidence that humans evolved very slow body growth to free up energy for our unusually costly brain development. In addition, the finding that the peak in brain energy needs occurs after the age of weaning in most traditional small-scale societies shows that much of the energetic costs of human brain development are not provided by maternal metabolism, but by social provisioning and allocare.
