Lack of Support for the Association between Facial Shape and Aggression: A Reappraisal Based on a Worldwide Population Genetics Perspective

Antisocial and criminal behaviors are multifactorial traits whose interpretation relies on multiple disciplines. Since these interpretations may have social, moral and legal implications, a constant review of the evidence is necessary before any scientific claim is considered as truth. A recent study proposed that men with wider faces relative to facial height (fWHR) are more likely to develop unethical behaviour mediated by a psychological sense of power. This research was based on reports suggesting that sexual dimorphism and selection would be responsible for a correlation between fWHR and aggression. Here we show that 4,960 individuals from 94 modern human populations belonging to a vast array of genetic and cultural contexts do not display significant amounts of fWHR sexual dimorphism. Further analyses using populations with associated ethnographical records as well as samples of male prisoners of the Mexico City Federal Penitentiary condemned by crimes of variable level of inter-personal aggression (homicide, robbery, and minor faults) did not show significant evidence, suggesting that populations/individuals with higher levels of bellicosity, aggressive behaviour, or power-mediated behaviour display greater fWHR. Finally, a regression analysis of fWHR on individual''s fitness showed no significant correlation between this facial trait and reproductive success. Overall, our results suggest that facial attributes are poor predictors of aggressive behaviour, or at least, that sexual selection was weak enough to leave a signal on patterns of between- and within-sex and population facial variation.     

Evolutionary constraints of warning signals: A genetic trade‐off between the efficacy of larval and adult warning coloration can maintain variation in signal expression

To predict evolutionary responses of warning signals under selection, we need to determine the inheritance pattern of the signals, and how they are genetically correlated with other traits contributing to fitness. Furthermore, protective coloration often undergoes remarkable changes within an individual's lifecycle, requiring us to quantify the genetic constraints of adaptive coloration across all the relevant life stages. Based on a 12 generation pedigree with > 11,000 individuals of the wood tiger moth (Arctia plantaginis), we show that high primary defense as a larva (large warning signal) results in weaker defenses as adult (less efficient warning color), due to the negative genetic correlation between the efficacy of larval and adult warning coloration. However, production of effective warning coloration as a larva did not incur any life‐history costs and was positively genetically correlated with reproductive output. These results provide novel insights into the evolutionary constraints on protective coloration in animals, and explain the maintenance of variation in the signal expression despite the strong directional selection by predators. By analyzing the genetic and environmental effects on warning signal and life‐history traits in all relevant life stages, we can accurately determine the mechanisms shaping the evolutionary responses of phenotypic traits under different selection environments.     

Testosterone responses to competition in men are related to facial masculinity

Relationships between androgens and the size of sexually dimorphic male traits have been demonstrated in several non-human species. It is often assumed that a similar relationship exists for human male faces, but clear evidence of an association between circulating testosterone levels and the size of masculine facial traits in adulthood is absent. Here we demonstrate that, after experimentally determined success in a competitive task, men with more a masculine facial structure show higher levels of circulating testosterone than men with less masculine faces. In participants randomly allocated to a 'winning' condition, testosterone was elevated relative to pre-task levels at 5 and 20 min post-task. In a control group of participants allocated to a 'losing' condition there were no significant differences between pre- and post-task testosterone. An index of facial masculinity based on the measurement of sexually dimorphic facial traits was not associated with pre-task (baseline) testosterone levels, but was associated with testosterone levels 5 and 20 min after success in the competitive task. These findings indicate that a man's facial structure may afford important information about the functioning of his endocrine system.     

The relative importance of intra- and intersexual selection on human male sexually dimorphic traits

Recent evidence suggests that in sexual selection on human males, intrasexual competition plays a larger role than female choice. In a sample of men (N?=?164), we sought to provide further evidence on the effects of men's physical dominance and sexual attractiveness on mating success and hence in sexual selection. Objective measures and subjective ratings of male sexually dimorphic traits purportedly under sexual selection (height, vocal and facial masculinity, upper body size from 3D scans, physical strength, and baseline testosterone) and observer perceptions of physical dominance and sexual attractiveness based on self-presentation video recordings were assessed and associated with mating success (sociosexual behaviour and number of potential conceptions) in a partly longitudinal design. Results from structural equation models and selection analyses revealed that physical dominance, but not sexual attractiveness, predicted mating success. Physical dominance mediated associations of upper body size, physical strength, as well as vocal and facial physical dominance and attractiveness with mating success. These findings thus suggest a greater importance of intrasexual competition than female choice in human male sexual selection.     

Facial attractiveness and fertility in populations with low levels of modern birth control

Evolutionary models of human mate choice generally assume that physical attractiveness has evolved through sexual selection, i.e., it has been associated with higher mating opportunities and subsequent reproductive success across our evolutionary history. Here we investigate whether facial attractiveness is related to fertility in order to understand the extent to which selection can operate on attractive traits in modern populations. We used data from two populations where the prevalence of modern birth control methods is low and thus unlikely to disconnect mating opportunities from reproductive success: men and women from contemporary rural Senegal and men from the West Point Military Academy in the USA who graduated in 1950. We found that facial attractiveness negatively predicts age-specific reproduction in both sexes in Senegal and is independent from lifetime reproductive success in men from the USA. Overall, the results suggest that facial attractiveness is not under positive selection and raise questions about methodological approaches currently used to assess attractiveness.     

Behavioural changes and the adaptive diversification of pigeons and doves

What factors determine the extent of evolutionary diversification remains a major question in evolutionary biology. Behavioural changes have long been suggested to be a major driver of phenotypic diversification by exposing animals to new selective pressures. Nevertheless, the role of behaviour in evolution remains controversial because behavioural changes can also retard evolutionary change by hiding genetic variation from selection. In the present study, we apply recently implemented Ornstein–Uhlenbeck evolutionary models to show that behavioural changes led to associated evolutionary responses in functionally relevant morphological traits of pigeons and doves (Columbiformes). Specifically, changes from terrestrial to arboreal foraging behaviour reconstructed in a set of phylogenies brought associated shorter tarsi and longer tails, consistent with functional predictions. Interestingly, the transition to arboreality accelerated the rates of evolutionary divergence, leading to an increased morphological specialization that seems to have subsequently constrained reversals to terrestrial foraging. Altogether, our results support the view that behaviour may drive evolutionary diversification, but they also highlight that its evolutionary consequences largely depend on the limits imposed by the functional demands of the adaptive zone.     

The evolution of novel animal signals: silk decorations as a model system

Contemporary animal signals may derive from an elaboration of existing forms or novel non-signalling traits. Unravelling the evolution of the latter is challenging because experiments investigating the maintenance of the signal may provide little insight into its early evolution. The web decorations, or stabilimenta of some orb web spiders represent an intriguing model system to investigate novel animal signals. For over 100 years, biologists have struggled to explain why spiders decorate their webs with additional threads of silk, producing a conspicuous signal on a construction whose function is to entangle unsuspecting prey. The numerous explanations for the maintenance of this behaviour starkly contrast with the absence of a plausible explanation for its evolutionary origin. Our review highlights the difficulties in resolving both the evolution and maintenance of animal signalling, and inferring the causative arrow-even from experimental studies. Drawing on recent research that focuses on physiological processes, we provide a model of the evolutionary progression of web-decorating behaviour.     

Voice and handgrip strength predict reproductive success in a group of indigenous african females

Evolutionary accounts of human traits are often based on proxies for genetic fitness (e.g., number of sex partners, facial attractiveness). Instead of using proxies, actual differences in reproductive success is a more direct measure of Darwinian fitness. Certain voice acoustics such as fundamental frequency and measures of health such as handgrip strength correlate with proxies of fitness, yet there are few studies showing the relation of these traits to reproduction. Here, we explore whether the fundamental frequency of the voice and handgrip strength account for differences in actual reproduction among a population of natural fertility humans. Our results show that both fundamental frequency and handgrip strength predict several measures of reproductive success among a group of indigenous Namibian females, particularly amongst the elderly, with weight also predicting reproductive outcomes among males. These findings demonstrate that both hormonally regulated and phenotypic quality markers can be used as measures of Darwinian fitness among humans living under conditions that resemble the evolutionary environment of Homo sapiens. We also argue that these findings provide support for the Grandmother Hypothesis.     

On the inappropriate use of the naturalistic fallacy in evolutionary psychology

The naturalistic fallacy is mentionedfrequently by evolutionary psychologists as anerroneous way of thinking about the ethicalimplications of evolved behaviors. However,evolutionary psychologists are themselvesconfused about the naturalistic fallacy and useit inappropriately to forestall legitimateethical discussion. We briefly review what thenaturalistic fallacy is and why it is misusedby evolutionary psychologists. Then we attemptto show how the ethical implications of evolvedbehaviors can be discussed constructivelywithout impeding evolutionary psychologicalresearch. A key is to show how ethicalbehaviors, in addition to unethical behaviors,can evolve by natural selection.     

Self-Fulfilling Prophecies as a Link between Men’s Facial Width-to-Height Ratio and Behavior

The facial width-to-height ratio (fWHR) has been identified as a reliable predictor of men’s behavior, with researchers focusing on evolutionary selection pressures as the underlying mechanism explaining these relationships. In this paper, we complement this approach and examine the extent to which social processes also determine the extent to which men’s fWHR serves as a behavioral cue. Specifically, we propose that observers’ treatment of target men based on the targets’ fWHR subsequently affects behavior, leading the targets to behave in ways that are consistent with the observers’ expectations (i.e., a self-fulfilling prophecy). Results from four studies demonstrate that individuals behave more selfishly when interacting with men with greater fWHRs, and this selfish behavior, in turn, elicits selfish behavior in others.     

Extended phenotypes as signals

Animal signals may result from construction behaviour and can provide receivers with essential information in various contexts. Here we explore the potential benefits of extended phenotypes with a signalling function as compared to bodily ornaments and behavioural displays. Their independence of the body, their physical persistence and the morphological and cognitive conditions required for their construction allow unique communication possibilities. We classify various levels of information transfer by extended phenotype signals and explore the differences between secreted signals and signals resulting from collection and construction, which usually involve higher behavioural complexity. We examine evolutionary pathways of extended phenotypes with a signalling function with help of a comparative evaluation and conclude that often constructions first provide a direct fitness benefit, with a signalling function becoming more and more prominent during evolutionary progression. The abundance and variability of extended phenotypes as signals is impressive and provides unique possibilities for animal communication research.     

You're not my type: Do conservatives have a bias for seeing long-term mates?

When choosing a mate, humans favour genetic traits (attractiveness, high sex drive) for short-term relationships and parental traits (warmth, high status) for long-term relationships. These preferences serve to maximise fitness of future offspring. But this model neglects the role of social norms in shaping evolved mating strategies. For example, in conservative cultures, individuals are likely to face costs such as punishment for short-term mating. Here we show that conservatives over-perceive some mates' suitability as long-term partners. Study 1 found that conservatives were less likely to use a short-term strategy that was distinctive from their long-term strategy. Study 2 showed that conservatives over-perceived hypothetical mates as long-term investing partners, despite their lack of commitment-compatible traits. Conservatism was measured at the regional- (India, USA, UK) and individual-level. Our results demonstrate how social norms may bias behaviour. We anticipate our findings to be a starting point for more sophisticated models, drawing on developments from evolutionary and social psychology.     

An investigation of the evolutionary origin of reciprocal communication using simulated autonomous agents

How does communication originates in a population of originally non-communicating individuals? Providing an answer to this question from a neo-Darwinian epistemological perspective is not a trivial task. The reason is that, for non-communicating agents, the capabilities of emitting signals and responding to them are both adaptively neutral traits if they are not simultaneously present. Research studies based on rather general and theoretically oriented evolutionary simulation models have, so far, demonstrated that at least two different processes can account for the origin of communication. On the one hand, communicative behaviour may first evolve in a non-communicative context and only subsequently acquire its adaptive function. On the other hand, communication may originate thanks to cognitive constraints; that is, communication may originate thanks to the existence of neural substrates that are common to the signalling and categorising capabilities. This article provides a proof-of-concept demonstration of the origin of communication in a novel-simulated scenario in which groups of two homogeneous (i.e. genetically identical) agents exploit reciprocal communication to develop common perceptual categories and to perform a collective task. In particular, in circumstances in which communication is evolutionarily advantageous, simulated agents evolve from scratch social behaviour through acoustic interactions. We look into the phylogeny of successful communication protocol, and we describe the evolutionary phenomena that, in early evolutionary stages, paved the way for the subsequent development of reciprocal communication, categorisation capabilities and successful cooperative strategies.     

Accidental experiments: ecological and evolutionary insights and opportunities derived from global change

Humans are the dominant ecological and evolutionary force on the planet today, transforming habitats, polluting environments, changing climates, introducing new species, and causing other species to decline in number or go extinct. These worrying anthropogenic impacts, collectively termed global change, are often viewed as a confounding factor to minimize in basic studies and a problem to resolve or quantify in applied studies. However, these ‘accidental experiments’ also represent opportunities to gain fundamental insight into ecological and evolutionary processes, especially when they result in perturbations that are large or long in duration and difficult or unethical to impose experimentally. We demonstrate this by describing important fundamental insights already gained from studies which utilize global change factors as accidental experiments. In doing so, we highlight why accidental experiments are sometimes more likely to yield insights than traditional approaches. Next, we argue that emerging environmental problems can provide even more opportunities for scientific discovery in the future, and provide both examples and guidelines for moving forward. We recommend 1) a greater flow of information between basic and applied subfields of ecology and evolution to identify emerging opportunities; 2) considering the advantages of the ‘accidental experiment’ approach relative to more traditional approaches; and 3) planning for the challenges inherent to uncontrolled accidental experiments. We emphasize that we do not view the accidental experiments provided by global change as replacements for scientific studies quantifying the magnitude of anthropogenic impacts or outlining strategies for mitigating impacts. Instead, we believe that accidental experiments are uniquely situated to provide insights into evolutionary and ecological processes that ultimately allow us to better predict and manage change on our human‐dominated planet. Synthesis Humans have an increasingly large impact on the planet. In response, ecologists and evolutionary biologists are dedicating increasing scientific attention to global change, largely with studies documenting biological effects and testing strategies to avoid or reverse negative impacts. In this article, we analyze global change from a different perspective, and suggest that human impacts on the environment also serve as valuable ‘accidental experiments’ that can provide fundamental scientific insight. We highlight and synthesize examples of studies taking this approach, and give guidance for gaining future insights from these unfortunate ‘accidental experiments’.     

Is cooperativeness readable in static facial features? An inter-cultural approach

There is evidence in the literature that non-verbal physical features are used as cues for a propensity to cooperate. However, further studies of the human ability to visually detect cooperativeness are required. In particular, the existence of static facial cues of altruism remains questionable. Moreover, an investigation of both sex differences and cross-cultural applicability with respect to altruism detection skills is crucial in the context of the evolution of human cooperation. In this study, we used both a public good game and a charitable contribution to assess the cooperativeness of 156 men and 172 women in rural Senegal and took facial photographs of these individuals. The second portion of the study was conducted in France. In total, 194 men and 171 women were asked to distinguish the most and least selfish individual from a series of 80 pairs of Senegalese facial photographs, each pair consisting of the highest and the lowest contributor from a group in the public good game. Using mixed modeling techniques, we controlled for facial masculinity, age and socio-economic status. For male pairs, both male and female French raters were able to identify more often than by chance which individual made the smallest contribution to the public good in each group; however, detection was not successful with female faces. These results suggest that sex-specific traits are involved and that only male facial traits indicating cooperative skills are, at least inter-culturally, readable. The specific facial traits involved are investigated. However, the charitable contribution was not correlated with the contribution to the public good, and further work is necessary to identify which specific altruistic traits are detectable and to assess the generality of these results.     

Stabilizing selection and adaptive evolution in a combination of two traits in an arctic ungulate

Stabilizing selection is thought to be common in wild populations and act as one of the main evolutionary mechanisms, which constrain phenotypic variation. When multiple traits interact to create a combined phenotype, correlational selection may be an important process driving adaptive evolution. Here, we report on phenotypic selection and evolutionary changes in two natal traits in a semidomestic population of reindeer (Rangifer tarandus) in northern Finland. The population has been closely monitored since 1969, and detailed data have been collected on individuals since they were born. Over the length of the study period (1969–2015), we found directional and stabilizing selection toward a combination of earlier birth date and heavier birth mass with an intermediate optimum along the major axis of the selection surface. In addition, we demonstrate significant changes in mean traits toward earlier birth date and heavier birth mass, with corresponding genetic changes in breeding values during the study period. Our results demonstrate evolutionary changes in a combination of two traits, which agree closely with estimated patterns of phenotypic selection. Knowledge of the selective surface for combinations of genetically correlated traits are vital to predict how population mean phenotypes and fitness are affected when environments change.     

Sensation seeking and men's face preferences

Findings from previous studies suggest that only men who are in good physical condition can afford to pursue high-risk activities and that men who engage in high-risk activities are considered particularly attractive by women. Here, we show that men's interest in high-sensation activities, a personality trait that is known to increase the likelihood of those individuals engaging in high-risk behaviors, is positively related to the strength of their preferences for femininity in women's faces (Studies 1–3) but is not related to the strength of their preferences for femininity in men's faces (Study 2). We discuss these findings as evidence for potentially adaptive condition-dependent mate preferences, whereby men who exhibit signals of high quality demonstrate particularly strong preferences for facial cues of reproductive and medical health in potential mates because they are more likely than lower-quality men to succeed in acquiring such partners.     

Molecular mechanisms of floral mimicry in orchids

Deceptive plants do not produce floral rewards, but attract pollinators by mimicking signals of other organisms, such as food plants or female insects. Such floral mimicry is particularly common in orchids, in which flower morphology, coloration and odour play key roles in deceiving pollinators. A better understanding of the molecular bases for these traits should provide new insights into the occurrence, mechanisms and evolutionary consequences of floral mimicry. It should also reveal the molecular bases of pollinator-attracting signals, in addition to providing strategies for manipulating insect behaviour in general. Here, we review data on the molecular bases for traits involved in floral mimicry, and we describe methodological advances helpful for the functional evaluation of key genes.     

Low heritabilities, but genetic and maternal correlations between red squirrel behaviours

Consistent individual differences in behaviour, and behavioural correlations within and across contexts, are referred to as animal personalities. These patterns of variation have been identified in many animal taxa and are likely to have important ecological and evolutionary consequences. Despite their importance, genetic and environmental sources of variation in personalities have rarely been characterized in wild populations. We used a Bayesian animal model approach to estimate genetic parameters for aggression, activity and docility in North American red squirrels (Tamiasciurus hudsonicus). We found support for low heritabilities (0.08-0.12), and cohort effects (0.07-0.09), as well as low to moderate maternal effects (0.07-0.15) and permanent environmental effects (0.08-0.16). Finally, we found evidence of a substantial positive genetic correlation (0.68) and maternal effects correlation (0.58) between activity and aggression providing evidence of genetically based behavioural correlations in red squirrels. These results provide evidence for the presence of heritable variation in red squirrel behaviour, but also emphasize the role of other sources of variation, including maternal effects, in shaping patterns of variation and covariation in behavioural traits.