Carel P van Schaik

University of Zurich | UZH · Department of Evolutionary Anthropology

Although cumulative culture is a hallmark of hominin evolution, its origins can be traced back to our common ancestor with chimpanzees. Here, we investigated the evolutionary origins of chimpanzee cumulative culture and why it remained incipient. To trace cultural transmission among the four chimpanzee subspecies, we compared population networks ba...

There is tremendous taxonomic variation in the size, shape, and structure of vertebrate brains. While many studies aim at identifying the ecological factors (social and environmental) that explain brain size variation within taxa, a more fundamental divide exists between endotherm and ectotherm vertebrates. Ectotherms have ten times smaller brains...

Brain size varies greatly across and even within lineages. Attempts to explain this variation have mostly focused on the role of specific cognitive demands in the social or ecological domain. However, their predictive power is modest, whereas the effects of additional functions, especially sensory information processing and motor control, on brain...

Brain size variability in primates has been attributed to various domain-specific socio-ecological factors. A recently published large-scale study of short-term memory abilities in 41 primate species (ManyPrimates 2022 Anim. Behav. Cogn. 9, 428–516. (doi:10.26451/abc.09.04.06.2022)) did not find any correlations with 11 different proxies of externa...

Theoretical and empirical scholars of cultural evolution have traditionally studied social learning strategies, such as conformity, as adaptive strategies to obtain accurate information about the environment, whereas within social psychology there has been a greater focus upon the social consequences of such strategies. Although these two approache...

Keywords: needing to learn hypothesis nest-building behaviour ontogeny selectivity skill learning Sumatran orang-utan trial-and-error practice Nest building is an important subsistence behaviour that young great apes must learn to become competent adults. Orang-utans show a remarkable degree of variability and selectivity for a broad range of featu...

Humans and many other animal species act in ways that benefit others. Such prosocial behaviour has been studied extensively across a range of disciplines over the last decades, but findings to date have led to conflicting conclusions about prosociality across and even within species. Here, we present a conceptual framework to study the proximate re...

Brain size variability in primates has been attributed to various domain-specific socio-ecological factors. A recently published large-scale study of short-term memory abilities in 41 primate species [1] did not find any correlations with 11 different proxies of external cognitive demands. Here we found that the interspecific variation in test perf...

In many group-living species, individuals are required to flexibly modify their communicative behaviour in response to current social challenges. To unravel whether sociality and communication systems co-evolve, research efforts have often targeted the links between social organisation and communicative repertoires. However, it is still unclear whi...

Vertebrate brains show extensive variation in relative size. The expensive brain hypothesis argues that one important source of this variation is linked to a species’ ability to generate the energy required to sustain the brain, especially during periods of unavoidable food scarcity. Here we ask whether this hypothesis, tested so far in endothermic...

The social and mating systems of orangutans, one of our closest relatives, remain poorly understood. Orangutans (Pongo spp.) are highly sexually dimorphic and females are philopatric and maintain individual, but overlapping home ranges, whereas males disperse, are non-territorial and wide-ranging, and show bimaturism, with many years between reachi...

While cumulative culture is a hallmark of hominin evolution, its origins can be traced back to our common ancestor with chimpanzees. Here we investigate the evolutionary origins of chimpanzee cumulative culture, and why it remained incipient. To trace cultural transmission among the four chimpanzee subspecies, we built between-populations networks...

In many slowly developing mammal species, males reach sexual maturity well before they develop secondary sexual characteristics. Sexually mature male orangutans have exceptionally long periods of developmental arrest. The two male morphs have been associated with behavioral alternative reproductive tactics, but this interpretation is based on cross...

Large brains provide adaptive cognitive benefits but require unusually high, near-constant energy inputs and become fully functional well after their growth is completed. Consequently, young of most larger-brained endotherms should not be able to independently support the growth and development of their own brains. This paradox is solved if the evo...

Heintz & Scott-Phillips propose that the partner choice ecology of our ancestors required Gricean cognitive pragmatics for reputation management, which caused a tendency toward showing and expecting prosociality that subsequently scaffolded language evolution. Here, we suggest a cognitively leaner explanation that is more consistent with comparativ...

Proactive information donation is crucial for human cumulative cultural evolution. Evidence for proactive information donation in nonhuman animals is limited to a few examples, and its evolutionary origin remains debated. Here, we examine the role of cooperative breeding for the evolution of proactive information donation by comparing cooperatively...

Large brains support numerous cognitive adaptations and therefore may appear to be highly beneficial. Nonetheless, the high energetic costs of brain tissue may have prevented the evolution of large brains in many species. This problem may also have a developmental dimension: juveniles, with their immature and therefore poorly performing brains, wou...

Human hyper-cooperativity and the emergence of division of labor enables us to not only solve problems effectively within a group but also collectively. Collective problem solving occurs when groups perform better than the additive performance of separate individuals. Currently, it is unknown whether this is unique to humans. To investigate the evo...

Orangutan females live semi-solitarily, spending 50–80 percent of their time alone, with only their dependent offspring for company (van Schaik, 1999). They are philopatric (Arora et al., 2012; van Noordwijk et al., 2002) and establish their home ranges in an area that overlaps with their natal range as well as with those of other females, both mat...

Communicative repair is a fundamental and universal element of interactive language use. It has been suggested that the persistence and elaboration after communicative breakdown in nonhuman primates constitute two evolutionary building blocks of this capacity, but the conditions favouring it are poorly understood. Because zoo-housed individuals of...

To understand the primate origins of the human interaction engine, it is worthwhile to focus not only on great apes but also on callitrichid monkeys (marmosets and tamarins). Like humans, but unlike great apes, callitrichids are cooperative breeders, and thus habitually engage in coordinated joint actions, for instance when an infant is handed over...

Across the animal kingdom, we see remarkable variation in brain size. This variation has even increased over evolutionary time. Traditionally, studies aiming to explain brain size evolution have looked at the fitness benefits of increased brain size in relation to its increased cognitive performance in the social and/or ecological domain. However,...

Between-individual variation in behavioural expression, such as social responsiveness, has been shown to have important eco-evolutionary consequences. However, most comparative research on non-human primate communication has focused on species- or population-level variation, while among- and within-individual variation has been largely ignored or c...

Humans communicate with small children in unusual and highly conspicuous ways (child-directed communication (CDC)), which enhance social bonding and facilitate language acquisition. CDC-like inputs are also reported for some vocally learning animals, suggesting similar functions in facilitating communicative competence. However, adult great apes, o...

In many group-living mammals, philopatric females form the stable core of the group and defend food or shelter against other groups of females. Where males are larger, their participation could give their female group the edge. How can females secure the contribution of males that are neither the father of current infants, nor the dominant male exp...

As climate change continues to fundamentally alter resource landscapes, the ability to flexibly respond to spatio-temporal changes in the distribution of preferred food sources is increasingly important for the overall health and fitness of animals living in seasonal, variable, and/or changing environments. Here, we investigate the effects of an un...

This paper surveys five human societal types – mobile foragers, horticulturalists, pre-state agriculturalists, state-based agriculturalists, and liberal democracies – from the perspective of three core social problems faced by interacting individuals: coordination problems, social dilemmas, and contest problems. We characterize the occurrence of th...

This paper surveys five human societal types -- mobile foragers, horticulturalists, pre-state agriculturalists, state-based agriculturalists, and liberal democracies -- from the perspective of three core social problems faced by interacting individuals: coordination problems, social dilemmas, and contest problems. We characterize the occurrence of...

Large brains support numerous cognitive adaptations and therefore may appear to be highly beneficial. Nonetheless, the high energetic costs of brain tissue may have prevented the evolution of large brains in many species. This problem may also have a developmental dimension: juveniles, with their immature and therefore poorly performing brains, wou...

Whether nonhuman species can change their communicative repertoire in response to socio-ecological environments has critical implications for communicative innovativeness prior to the emergence of human language, with its unparalleled productivity. Here, we use a comparative sample of wild and zoo-housed orang-utans of two species (Pongo abelii, P....

Scientists have long struggled to establish how larger brains translate into higher cognitive performance across species. While absolute brain size often yields high predictive power of performance, its positive correlation with body size warrants some level of correction. It is expected that larger brains are needed to control larger bodies withou...

In species in which adults of the two sexes show long‐term association, males often engage in acts of assistance (“services”) aimed at females and/or their young in various behavioural contexts that are not reciprocated. We conducted a quantitative review of the primate literature on sex differences in involvement in protection against predation. W...

From early infancy, human face-to-face communication is multimodal, comprising a plethora of interlinked communicative and sensory modalities. Although there is also growing evidence for this in nonhuman primates, previous research rarely disentangled production from perception of signals. Consequently, the functions of integrating articulators (i....

Both absolute and relative brain sizes vary greatly among and within the major vertebrate lineages. Scientists have long debated how larger brains in primates and hominins translate into greater cognitive performance, and in particular how to control for the relationship between the noncognitive functions of the brain and body size. One solution to...

To resolve the major controversy about why prosocial behaviors persist in large-scale human societies, we propose that two questions need to be answered. First, how do social interactions in small-scale and large-scale societies differ? By reviewing the exchange and collective-action dilemmas in both small-scale and large-scale societies, we show t...

To resolve the major controversy about why prosocial behaviors persist in large‐scale human societies, we propose that two questions need to be answered. First, how do social interactions in small‐scale and large‐scale societies differ? By reviewing the exchange and collective‐action dilemmas in both small‐scale and large‐scale societies, we show t...

As a part of growing up, immature orangutans must acquire vast repertoires of skills and knowledge, a process that takes several years of observational social learning and subsequent practice. Adult female and male orangutans show behavioral differences including sex-specific foraging patterns and male-biased dispersal. We investigated how these di...

Orangutans show a pronounced sexual dimorphism, with flanged males (i.e., males with fully grown secondary sexual characteristics) reaching twice the size of adult females. Furthermore, adult orangutans show sex-specific dispersal and activity patterns. This study investigates sex differences in adult foraging behavior and sheds light on how these...

Both absolute and relative brain size vary greatly among and within the major vertebrate lineages. Scientists have long debated how larger brains in primates and hominins translate into greater cognitive performance, and in particular how to control for the relationship between the non-cognitive functions of the brain and body size. One solution to...

There are two well-established facts about vertebrate brains: brains are physiologically costly organs, and both absolute and relative brain size varies greatly between and within the major vertebrate clades. While the costs are relatively clear, scientists struggle to establish how larger brains translate into higher cognitive performance. Part of...

The creation of novel communicative acts is an essential element of human language. Although some research suggests the presence of this ability in great apes, this claim remains controversial. Here, we use orang-utans (Pongo spp.) to systematically assess the effect of the wild-captive contrast on the repertoire size of communicative acts. We find...

Social tolerance in a group reflects the balance between within-group competition and interdependence: whereas increased competition leads to a reduction in social tolerance, increased interdependence increases it. Captivity reduces both feeding competition and interdependence and can therefore affect social tolerance. In independently breeding pri...

Sexual coercion, in the form of forced copulations, is relatively frequently observed in orangutans and generally attributed to their semi-solitary lifestyle. High ecological costs of association for females may be responsible for this lifestyle and may have prevented the evolution of morphological fertility indicators (e.g., sexual swellings), whi...

From early infancy, human face-to-face communication is “multimodal”, comprising a plethora of interlinked articulators and sensory modalities. Although there is also growing evidence for this in nonhuman primates, the functions of integrating articulators (i.e. multiplex or multi-articulator acts) and channels (i.e. multimodal or multi-sensory act...

The zone of latent solutions (ZLS) hypothesis provides an alternative approach to explaining cultural patterns in primates and many other animals. According to the ZLS hypothesis, non-human great ape (henceforth: ape) cultures consist largely or solely of latent solutions. The current competing (and predominant) hypothesis for ape culture argues in...

The uniquely enlarged noses of male proboscis monkeys are prominent adornments, and a sexually selected male trait. A recent study showed significant correlations among nose, body, and testis sizes and clear associations between nose size and the number of females in a male's harem. However, to date, the analyses of other common male traits, i.e.,...

Primates, like other mammals, exhibit an annual reproductive pattern that ranges from strictly seasonal breeding to giving birth in all months of the year, but factors mediating this variation are not fully understood. We applied both a categorical description and quantitative measures of the birth peak breadth based on daily observations in zoos t...

Neural development is highly conserved across distantly related species of different brain sizes. Here, we show that the development of manipulative complexity is equally cumulative across 36 primate species and also that its ontogeny recapitulates phylogeny. Furthermore, larger-brained species reach their adult skill levels later than smaller-brai...

Dieses Themenheft unserer Sitzungsberichte ist das Ergebnis der Jahrestagung der Gesellschaft Naturforschender Freunde zu Berlin Anfang Juni 2016. Der Bogen spannt sich von der Phylogenie und Genetik bis zu einem spezifischen Parasiten als Teil unserer Umwelt. Doch liegt der Schwerpunkt in der Auseinandersetzung mit den Fragen danach, was uns zum M...

The potential for rituals in non-human great apes (apes) is an understudied topic. We derive a minimal definition of ritual and then examine the currently available evidence for it in untrained and non-enculturated apes. First, we examine whether such apes show evidence for the two main components of our minimal definition of ritual: symbolism and...

Most human societies exhibit a distinct class structure, with an elite, middle classes, and a bottom class, whereas animals form simple dominance hierarchies in which individuals with higher fighting ability do not appear to form coalitions to “oppress” weaker individuals. Here, we extend our model of primate coalitions and find that a division int...

Marmoset monkeys show high levels of proactive prosociality, a trait shared with humans, presumably because both species rely on allomaternal care. However, it is not clear whether the proximate regulation of this convergent trait is also similar, in particular with regard to intentionality, which is a defining characteristic of prosocial behavior...

Female orangutans exhibit natal philopatry, living in stable home ranges that overlap with those of their maternal relatives. Using data collected from 2003 to 2017 at Tuanan in Central Kalimantan, Indonesia, we take a longitudinal approach to better understand the mechanisms of female philopatry and the factors that influence the home range establ...

While signals in evolutionary biology are usually defined as “acts or traits that have evolved because of their effect on others”, work on gestures and vocalizations in various animal taxa have revealed population‐ or even individual‐specific meanings of social signals. These results strongly suggest that communicative acts that are like signals wi...

Exploration is essential for skill acquisition and strongly facilitates cognitive performance. In humans, it is widely known that exploration and later cognitive performance are highly dependent on early social inputs. Here, we aim to shed light on the evolutionary roots of this process by studying the effects of variation in opportunities for soci...

Cultural anthropology and evolutionary biology arose around the same time, and both adopted the same evolutionist framework. Their paths soon diverged, however, largely because anthropology rejected the notion of evolutionary progress—and thus the notion of the existence of primitive versus advanced races—before evolutionary biology did. Most anthr...

An understanding of ape culture o|ers important insights into the evolution of human culture. This chapter presents the argument that ape tool cultures consist of socially-mediated branching chains of individually-derived behaviors (‘latent solutions’) and presents the hypothesis that the evolved motivations and skills of apes potentially enable th...

The uniquely enlarged noses of male proboscis monkeys (Nasalis larvatus) are prominent adornments, and a sexually selected male masculine trait, as recently revealed by the significant correlations among nose, body, and testis sizes and the clear association between nose size and the number of females in a male's harem. However, till date, the anal...

Vorrede | In diesem charakteristischerweise hervorragend recherchierten Beitrag erörtern Kappeler und Fichtel die Konsequenzen sozialer und einkommensbedingter Ungleichheit für die individuelle Gesundheit und die empfundene Einsamkeit aus einer evolutionären Perspektive. Das zentrale Argument der Autoren ist, dass sich die modernen Großgesellschaft...

In this chapter, we apply the affective social learning (ASL) concept to the social learning of natural skill sets in immature orang-utans since it can serve as an illustration of the majority of learning that occurs in wild apes. Most orang-utan social learning happens during everyday tasks and without any active involvement of the role model. Con...

This chapter explores the notion that the behavioural and cognitive constituents of human social norms have equivalents or precursors in humans’ closest living relatives, the non-human primates. Scrutiny of the definitions of various forms of conformity revealed, on the one hand, that some key features defining social norms are essentially impossib...

Normative behavior is a human universal that is intimately linked to morality. Morality is an adaptation to the specifically human subsistence niche of hunting and gathering, which is skill-intensive and therefore relies on transmission of opaque knowledge and involves critical interdependence, reliance on coordinated division of labor, and synchro...

The communicative function of primates' self-directed behaviours like scratching has gained increasing attention in recent years, but their intentional use is still debated. Here, we addressed this issue by exploring the communicative function of 'loud scratches' in wild Sumatran orangutans. Building on previous studies in chimpanzees, we examined...

Wir zeichnen nach, auf welchen Wegen sich die kulturelle Evolution des Monotheismus vollzog. Die angeborenen Eigenarten des menschlichen Denkens bilden die Grundlage für die Entwicklung von Religionen. Dazu gehören unser Dualismus (der Geist ist unabhängig vom Körper) und unsere Neigung, alle Kausalität sozial, das heißt alle Ereignisse als Handlun...

Housing primates in naturalistic groups provides social benefits relative to solitary housing. However, food intake may vary across individuals, possibly resulting in overweight and underweight individuals. Information on relative adiposity (the amount of fat tissue relative to body weight) is needed to monitor overweight and underweight of group-h...

The presence of divergent and independent research traditions in the gestural and vocal domains of primate communication has resulted in major discrepancies in the definition and operationalization of cognitive concepts. However, in recent years, accumulating evidence from behavioural and neurobiological research has shown that both human and non‐h...

The expensive brain hypothesis predicts that the lowest stable level of energy input sets the upper limit to a species’ brain size. This prediction receives comparative support from the effects of experienced seasonality (including hibernation) and diet quality on mammalian brain size. Here, we test another prediction, which concerns the temporal s...

For humans we implicitly assume that the way we do things is the product of social learning and thus cultural. For animals, this conclusion requires proof. Here, we first review the most commonly used procedure for documenting animal culture: the method of exclusion, which charts geographic behavioral variation between populations as evidence for c...

To resolve the major controversy about how large-scale societies could ever evolve and be maintained, we propose that two questions need to be answered. First, how do social interactions in small-scale and large-scale societies differ? By reviewing the exchange and collective-action dilemmas in both small-scale and large-scale societies, we show th...

“Self‐domestication” has been invoked to understand important aspects of human evolution, integrating physiological, behavioral, and morphological information in a novel way. It proposes that selection for reduced aggression on animals undergoing domestication provides a model for selection favoring prosocial behaviors in humans and for a set of se...

Many animals, and in particular great apes, show evidence of culture, in the sense of having multiple innovations in multiple domains whose frequencies are influenced by social learning. But only humans show strong evidence of complex, cumulative culture, which is the product of copying and the resulting effect of cumulative cultural evolution. The...

Background Integrating demography and adaptive evolution is pivotal to understanding the evolutionary history and conservation of great apes. However, little is known about the adaptive evolution of our closest relatives, in particular if and to what extent adaptions to environmental differences have occurred. Here, we used whole-genome sequencing...