Music production and its role in coalition signaling during foraging contexts in a hunter-gatherer society

Music is a cultural activity universally present in all human societies. Several hypotheses have been formulated to understand the possible origins of music and the reasons for its emergence. Here, we test two hypotheses: (1) the coalition signaling hypothesis which posits that music could have emerged as a tool to signal cooperative intent and signal strength of alliances and (2) music as a strategy to deter potential predators. In addition, we further explore the link between tactile cues and the propensity of mothers to sing toward infants. For this, we investigated the singing behaviors of hunter-gatherer mothers during daily foraging trips among the Mbendjele BaYaka in the Republic of the Congo. Although singing is a significant component of their daily activities, such as when walking in the forest or collecting food sources, studies on human music production in hunter-gatherer societies are mostly conducted during their ritual ceremonies. In this study, we collected foraging and singing behavioral data of mothers by using focal follows of five BaYaka women during their foraging trips in the forest. In accordance with our predictions for the coalition signaling hypothesis, women were more likely to sing when present in large groups, especially when group members were less familiar. However, predictions of the predation deterrence hypothesis were not supported as the interaction between group size and distance from the village did not have a significant effect on the likelihood of singing. The latter may be due to limited variation in predation risk in the foraging areas, because of the intense bush meat trade, and hence, future studies should include foraging areas with higher densities of wild animals. Lastly, we found that mothers were more likely to sing when they were carrying infants compared to when infants were close, but carried by others, supporting the prediction that touch plays an important prerequisite role in musical interaction between the mother and child. Our study provides important insight into the role of music as a tool in displaying the intent between or within groups to strengthen potentially conflict-free alliances during joint foraging activities.

The adaptive significance of human scleral brightness: an experimental study

Homogeneously depigmented sclerae have long been proposed to be uniquely human-an adaptation to enable cooperative behaviour by facilitating interpersonal coordination through gaze following. However, recent evidence has shown that deeply pigmented sclerae also afford gaze following if surrounding a bright iris. Furthermore, while current scleral depigmentation is clearly adaptive in modern humans, it is less clear how the evolutionarily intermediate stages of scleral pigmentation may have been adaptive. In sum, it is unclear why scleral depigmentation became the norm in humans, while not so in sister species like chimpanzees, or why some extant species display intermediate degrees of pigmentation (as our ancestors presumably did at some point). We created realistic facial images of 20 individually distinct hominins with diverse facial morphologies, each face in the (i) humanlike bright sclera and (ii) generalised apelike dark sclera version. Participants in two online studies rated the bright-sclera hominins as younger, healthier, more attractive and trustworthy, but less aggressive than the dark-sclera hominins. Our results support the idea that the appearance of more depigmented sclerae promoted perceived traits that fostered trust, increasing fitness for those individuals and resulting in depigmentation as a fixed trait in extant humans.

The Biological Roots of Music and Dance : Extending the Credible Signaling Hypothesis to Predator Deterrence

After they diverged from panins, hominins evolved an increasingly committed terrestrial lifestyle in open habitats that exposed them to increased predation pressure from Africa's formidable predator guild. In the Pleistocene, Homo transitioned to a more carnivorous lifestyle that would have further increased predation pressure. An effective defense against predators would have required a high degree of cooperation by the smaller and slower hominins. It is in the interest of predator and potential prey to avoid encounters that will be costly for both. A wide variety of species, including carnivores and apes and other primates, have therefore evolved visual and auditory signals that deter predators by credibly signaling detection and/or the ability to effectively defend themselves. In some cooperative species, these predator deterrent signals involve highly synchronized visual and auditory displays among group members. Hagen and Bryant (Human Nature, 14(1), 21-51, 2003) proposed that synchronized visual and auditory displays credibly signal coalition quality. Here, this hypothesis is extended to include credible signals to predators that they have been detected and would be met with a highly coordinated defensive response, thereby deterring an attack. Within-group signaling functions are also proposed. The evolved cognitive abilities underlying these behaviors were foundations for the evolution of fully human music and dance.

Predicting strength from aggressive vocalizations versus speech in African bushland and urban communities

The human voice carries information about a vocalizer's physical strength that listeners can perceive and that may influence mate choice and intrasexual competition. Yet, reliable acoustic correlates of strength in human speech remain unclear. Compared to speech, aggressive nonverbal vocalizations (roars) may function to maximize perceived strength, suggesting that their acoustic structure has been selected to communicate formidability, similar to the vocal threat displays of other animals. Here, we test this prediction in two non-WEIRD African samples: an urban community of Cameroonians and rural nomadic Hadza hunter-gatherers in the Tanzanian bushlands. Participants produced standardized speech and volitional roars and provided handgrip strength measures. Using acoustic analysis and information-theoretic multi-model inference and averaging techniques, we show that strength can be measured from both speech and roars, and as predicted, strength is more reliably gauged from roars than vowels, words or greetings. The acoustic structure of roars explains 40-70% of the variance in actual strength within adults of either sex. However, strength is predicted by multiple acoustic parameters whose combinations vary by sex, sample and vocal type. Thus, while roars may maximally signal strength, more research is needed to uncover consistent and likely interacting acoustic correlates of strength in the human voice. This article is part of the theme issue 'Voice modulation: from origin and mechanism to social impact (Part I)'.

Disguises and the Origins of Clothing

Thermoregulation is often thought to be a key motivating factor behind the origins of clothing. Less attention has been given, however, to the production and use of clothing across traditional societies in contexts outside of thermoregulatory needs. Here I investigate the use of disguises, modesty coverings, and body armor among the 10 hunter-gatherer societies in the Probability Sample Files (PSF) within the Human Relations Area Files (HRAF) World Cultures database, with a particular focus on disguise cases and how they compare with strategies of deception across other taxa. The employment of disguises-defined as altering one's appearance for purposes of deceiving conspecifics or other animals-is noted for eight of the 10 societies, with their use occurring in contexts of hunting, religious or cult practices, and war or interpersonal violence. Most hunter-gatherer disguises demonstrated clear similarities to cases of visual deception found in other species, with the majority of examples fitting categories of animal mimicry, masquerading as plants, disruptive coloration (camouflage), or background matching (camouflage), while disguises unique to humans involved the impersonation of culture-specific "spirit-beings." Clothing for modesty purposes (nine societies) and body armor (six societies) are also noted. I propose that strategic initiatives by individuals or groups to disguise or conceal themselves represents one possible initial pathway to the cultural evolution of clothing. There are likely multiple potential (nonexclusive) social and functional pathways to the emergence of clothing outside of thermoregulatory needs.

Human domestication and the roles of human agency in human evolution

Are humans a domesticated species? How is this issue related to debates on the roles of human agency in human evolution? This article discusses four views on human domestication: (1) Darwin's view; (2) the view of those who link human domestication to anthropogenic niche construction and, more specifically, to sedentism; (3) the view of those who link human domestication to selection against aggression and the domestication syndrome; and (4) a novel view according to which human domestication can be conceived of in terms of a process of political selection. The article examines and compares these views to illustrate how discussions of human domestication can contribute to debates about how, and to what extent, human agency has affected human evolution.