Mathias Osvath & Elin Karvonen
PLoS ONE, May 2012
Background: The ability to invent means to deceive others, where the deception lies in the perceptually or contextually detached future, appears to require the coordination of sophisticated cognitive skills toward a single goal. Meanwhile innovation for a current situation has been observed in a wide range of species. Planning, on the one hand, and the social cognition required for deception on the other, have been linked to one another, both from a co-evolutionary and a neuroanatomical perspective. Innovation and deception have also been suggested to be connected in their nature of relying on novelty.
Methodology/Principal Findings: We report on systematic observations suggesting innovation for future deception by a captive male chimpanzee (Pan troglodytes). As an extension of previously described behaviour - caching projectiles for later throwing at zoo visitors - the chimpanzee, again in advance, manufactured concealments from hay, as well as used naturally occurring concealments. All were placed near the visitors' observation area, allowing the chimpanzee to make throws before the crowd could back off. We observed what was likely the first instance of this innovation. Further observations showed that the creation of future-oriented concealments became the significantly preferred strategy. What is more, the chimpanzee appeared consistently to combine two deceptive strategies: hiding projectiles and inhibiting dominance display behaviour.
Conclusions/Significance: The findings suggest that chimpanzees can represent the future behaviours of others while those others are not present, as well as take actions in the current situation towards such potential future behaviours. Importantly, the behaviour of the chimpanzee produced a future event, rather than merely prepared for an event that had been reliably re-occurring in the past. These findings might indicate that the chimpanzee recombined episodic memories in perceptual simulations.
Aaron Kheifets & C.R. Gallistel
Proceedings of the National Academy of Sciences, forthcoming
Abstract: Animals successfully navigate the world despite having only incomplete information about behaviorally important contingencies. It is an open question to what degree this behavior is driven by estimates of stochastic parameters (brain-constructed models of the experienced world) and to what degree it is directed by reinforcement-driven processes that optimize behavior in the limit without estimating stochastic parameters (model-free adaptation processes, such as associative learning). We find that mice adjust their behavior in response to a change in probability more quickly and abruptly than can be explained by differential reinforcement. Our results imply that mice represent probabilities and perform calculations over them to optimize their behavior, even when the optimization produces negligible material gain.
Alon Keinan & Andrew Clark
Science, 11 May 2012, Pages 740-743
Abstract: Human populations have experienced recent explosive growth, expanding by at least three orders of magnitude over the past 400 generations. This departure from equilibrium skews patterns of genetic variation and distorts basic principles of population genetics. We characterized the empirical signatures of explosive growth on the site frequency spectrum and found that the discrepancy in rare variant abundance across demographic modeling studies is mostly due to differences in sample size. Rapid recent growth increases the load of rare variants and is likely to play a role in the individual genetic burden of complex disease risk. Hence, the extreme recent human population growth needs to be taken into consideration in studying the genetics of complex diseases and traits.
Jayson Lusk & Bailey Norwood
European Review of Agricultural Economics, April 2012, Pages 189-212
Abstract: Economists have long relied on utilitarian principles in carrying out cost-benefit analysis, but such utilitarianism is typically limited to the well-being of humans. Some prominent philosophers have argued such an approach is unjustifiably speciesist, but what are the consequences of including animal well-being in cost-benefit analysis? This paper considers this question in the context of human altruism towards animals in which people's concerns for the well-being of animals create an externality. After uncovering some conceptual challenges involved in carrying out cost-benefit analysis on animal welfare policies, we report the results of a novel experiment used to measure the public-good value of farm animal welfare, and show that although the average value in our sample is quite large, the result is due to the preferences of only a small subset of the subjects.
Journal of Women, Politics & Policy, Spring 2012, Pages 176-187
Abstract: This research note asks whether the gender of a landowner matters when it comes to endangered species conservation. Based on interviews with landowners in Ohio and Utah who share their property with endangered snakes or tortoises, it is argued that effective policy must confront existing gender differences. Women and men care equally about the tortoise in Utah while women care significantly less about the snake in Ohio. Moreover, women appear to extend an ethic of care to tortoises but not snakes. Thus, there is reason to believe that gender can matter and, when it does, policy needs to address this difference.
Elizabeth Archie, Jeanne Altmann & Susan Alberts
Proceedings of the National Academy of Sciences, forthcoming
Abstract: Social status can have striking effects on health in humans and other animals, but the causes often are unknown. In male vertebrates, status-related differences in health may be influenced by correlates of male social status that suppress immune responses. Immunosuppressive correlates of low social status may include chronic social stress, poor physical condition, and old age; the immunosuppressive correlates of high status may include high testosterone and energetic costs of reproduction. Here we test whether these correlates could create status-related differences in immune function by measuring the incidence of illness and injury and then examining healing rates in a 27-y data set of natural injuries and illnesses in wild baboon males. We found no evidence that the high testosterone and intense reproductive effort associated with high rank suppress immune responses. Instead, high-ranking males were less likely to become ill, and they recovered more quickly than low-ranking males, even controlling for differences in age. Notably, alpha males, who experience high glucocorticoids, as well as the highest testosterone and reproductive effort, healed significantly faster than other males, even other high-ranking males. We discuss why alpha males seem to escape from the immunosuppressive costs of glucocorticoids but low-ranking males do not, including the idea that glucocorticoids' effects depend on an individual's physiological and social context.
Pontus Skoglund et al.
Science, 27 April 2012, Pages 466-469
Abstract: The farming way of life originated in the Near East some 11,000 years ago and had reached most of the European continent 5000 years later. However, the impact of the agricultural revolution on demography and patterns of genomic variation in Europe remains unknown. We obtained 249 million base pairs of genomic DNA from ~5000-year-old remains of three hunter-gatherers and one farmer excavated in Scandinavia and find that the farmer is genetically most similar to extant southern Europeans, contrasting sharply to the hunter-gatherers, whose distinct genetic signature is most similar to that of extant northern Europeans. Our results suggest that migration from southern Europe catalyzed the spread of agriculture and that admixture in the wake of this expansion eventually shaped the genomic landscape of modern-day Europe.
Charles Perreault & Sarah Mathew
PLoS ONE, April 2012
Abstract: Language is a key adaptation of our species, yet we do not know when it evolved. Here, we use data on language phonemic diversity to estimate a minimum date for the origin of language. We take advantage of the fact that phonemic diversity evolves slowly and use it as a clock to calculate how long the oldest African languages would have to have been around in order to accumulate the number of phonemes they possess today. We use a natural experiment, the colonization of Southeast Asia and Andaman Islands, to estimate the rate at which phonemic diversity increases through time. Using this rate, we estimate that present-day languages date back to the Middle Stone Age in Africa. Our analysis is consistent with the archaeological evidence suggesting that complex human behavior evolved during the Middle Stone Age in Africa, and does not support the view that language is a recent adaptation that has sparked the dispersal of humans out of Africa. While some of our assumptions require testing and our results rely at present on a single case-study, our analysis constitutes the first estimate of when language evolved that is directly based on linguistic data.
Alexandre Courtiol et al.
Proceedings of the National Academy of Sciences, forthcoming
Abstract: Whether and how human populations exposed to the agricultural revolution are still affected by Darwinian selection remains controversial among social scientists, biologists, and the general public. Although methods of studying selection in natural populations are well established, our understanding of selection in humans has been limited by the availability of suitable datasets. Here, we present a study comparing the maximum strengths of natural and sexual selection in humans that includes the effects of sex and wealth on different episodes of selection. Our dataset was compiled from church records of preindustrial Finnish populations characterized by socially imposed monogamy, and it contains a complete distribution of survival, mating, and reproductive success for 5,923 individuals born 1760-1849. Individual differences in early survival and fertility (natural selection) were responsible for most variation in fitness, even among wealthier individuals. Variance in mating success explained most of the higher variance in reproductive success in males compared with females, but mating success also influenced reproductive success in females, allowing for sexual selection to operate in both sexes. The detected opportunity for selection is in line with measurements for other species but higher than most previous reports for human samples. This disparity results from biological, demographic, economic, and social differences across populations as well as from failures by most previous studies to account for variation in fitness introduced by nonreproductive individuals. Our results emphasize that the demographic, cultural, and technological changes of the last 10,000 y did not preclude the potential for natural and sexual selection in our species.
Noémie Becker et al.
Evolution and Human Behavior, forthcoming
Abstract: African pygmies' short stature has been studied for more than a century, but the evolution of this extreme phenotype remains unknown. The present study tests the hypothesis that sexual selection, through preference for short partners, may have contributed to the evolution of pygmies' stature. We gathered anthropometric and familial data from 72 Baka pygmy couples and 27 neighboring Nzimé nonpygmy couples from Cameroon. We found evidence for positive assortative mating and partial evidence for the male-taller norm in both groups. This is surprisingly close to results reported for many modern occidental populations, in which sexual selection is thought to exert a positive selective pressure on men height. Semistructured interviews of Baka pygmies concerning height and mate choice suggested that the male-taller norm matches mating preferences. Stature was also positively correlated with the number of serial marriages contracted by men of both populations, while the stature of women was not related to their mating success. Finally, we did not detect any linear or quadratic effect of height on reproductive success for either men or women. Altogether, our results demonstrate that stature influences mate choice in pygmies, and we argue that, if of any influence for sexual selection, mate choice should have favored tallness rather than shortness in our pygmy population. Consequently, this study establishes that sexual selection is a very unlikely candidate to account for the evolution of pygmies' short stature.
Susana Carvalho et al.
Current Biology, 20 March 2012, Pages R180-R181
Abstract: Why did our earliest hominin ancestors begin to walk bipedally as their main form of terrestrial travel? The lack of sufficient fossils and differing interpretations of existing ones leave unresolved the debate about what constitutes the earliest evidence of habitual bipedality. Compelling evidence shows that this shift coincided with climatic changes that reduced forested areas, probably forcing the earliest hominins to range in more open settings. While environmental shifts may have prompted the origins of bipedality in the hominin clade, it remains unknown exactly which selective pressures led hominins to modify their postural repertoire to include a larger component of bipedality. Here, we report new experimental results showing that wild chimpanzees walk bipedally more often and carry more items when transporting valuable, unpredictable resources to less-competitive places.
Jenny Tung et al.
Proceedings of the National Academy of Sciences, 24 April 2012, Pages 6490-6495
Abstract: Variation in the social environment is a fundamental component of many vertebrate societies. In humans and other primates, adverse social environments often translate into lasting physiological costs. The biological mechanisms associated with these effects are therefore of great interest, both for understanding the evolutionary impacts of social behavior and in the context of human health. However, large gaps remain in our understanding of the mechanisms that mediate these effects at the molecular level. Here we addressed these questions by leveraging the power of an experimental system that consisted of 10 social groups of female macaques, in which each individual's social status (i.e., dominance rank) could be experimentally controlled. Using this paradigm, we show that dominance rank results in a widespread, yet plastic, imprint on gene regulation, such that peripheral blood mononuclear cell gene expression data alone predict social status with 80% accuracy. We investigated the mechanistic basis of these effects using cell type-specific gene expression profiling and glucocorticoid resistance assays, which together contributed to rank effects on gene expression levels for 694 (70%) of the 987 rank-related genes. We also explored the possible contribution of DNA methylation levels to these effects, and identified global associations between dominance rank and methylation profiles that suggest epigenetic flexibility in response to status-related behavioral cues. Together, these results illuminate the importance of the molecular response to social conditions, particularly in the immune system, and demonstrate a key role for gene regulation in linking the social environment to individual physiology.
Elia Psouni, Axel Janke & Martin Garwicz
PLoS ONE, April 2012
Abstract: Our large brain, long life span and high fertility are key elements of human evolutionary success and are often thought to have evolved in interplay with tool use, carnivory and hunting. However, the specific impact of carnivory on human evolution, life history and development remains controversial. Here we show in quantitative terms that dietary profile is a key factor influencing time to weaning across a wide taxonomic range of mammals, including humans. In a model encompassing a total of 67 species and genera from 12 mammalian orders, adult brain mass and two dichotomous variables reflecting species differences regarding limb biomechanics and dietary profile, accounted for 75.5%, 10.3% and 3.4% of variance in time to weaning, respectively, together capturing 89.2% of total variance. Crucially, carnivory predicted the time point of early weaning in humans with remarkable precision, yielding a prediction error of less than 5% with a sample of forty-six human natural fertility societies as reference. Hence, carnivory appears to provide both a necessary and sufficient explanation as to why humans wean so much earlier than the great apes. While early weaning is regarded as essentially differentiating the genus Homo from the great apes, its timing seems to be determined by the same limited set of factors in humans as in mammals in general, despite some 90 million years of evolution. Our analysis emphasizes the high degree of similarity of relative time scales in mammalian development and life history across 67 genera from 12 mammalian orders and shows that the impact of carnivory on time to weaning in humans is quantifiable, and critical. Since early weaning yields shorter interbirth intervals and higher rates of reproduction, with profound effects on population dynamics, our findings highlight the emergence of carnivory as a process fundamentally determining human evolution.
Vincent Egan & Jason MacKenzie
Anthrozoos, June 2012, Pages 161-170
Abstract: The current study investigated the relationship between dimensions of personality, self-reports of delinquency, mating effort, and the desire to own a dog perceived as aggressive. Seven common breeds of dog were rated by 235 participants living within the UK and North America, using an online survey application. Participants also completed scales measuring personality, earlier delinquency, and mating effort. A clear dimension in perceived aggressiveness was found across dog breeds. Persons lower in Agreeableness, higher in Neuroticism and Conscientiousness, and of younger age actively preferred a dog perceived as aggressive. Neither delinquency nor mating effort actively predicted this preference for an aggressive dog, although these measures were themselves correlated with Agreeableness; a regression analysis found that low Agreeableness, younger age, and higher Conscientiousness predicted higher ratings on the aggression preference dimension. These findings show that a preference for a more aggressive dog is not necessarily driven by self-reported status display and intersexual competition so much as youth, low Agreeableness, and Conscientiousness generally.