Number of males in primate groups: Comparative tests of competing hypotheses

Primate social groups frequently contain multiple males. Male group size has been hypothesized to result from male mating competition, but the selective factors responsible for the evolution of multimale groups are unclear. Short breeding seasons create situations that are not conducive for single males to monopolize mating access to females, and may therefore favor the formation of large male groups. Alternatively, since the costs of mate defense increase with the spatial clumping of females, female group size may be a primary determinant of the number of males in a primate group. We used comparative methods designed to control for the potentially confounding effects of hidden third variables associated with phylogeny to test the breeding season and female group size hypotheses for the evolution of multimale groups. Our results revealed no association between breeding season duration and the number of males in groups. In contrast, we provide support for the female group size hypothesis by demonstrating a strong pattern of correlated evolution between female and male group size. © 1996 Wiley-Liss, Inc.     

Extractive foraging and the evolution of primate intelligence

One of the two major theories regarding the evolution of intelligence in primates is that feeding strategies determine mental development. Evidence for this theory is reviewed and related to extractive foraging, which is the act of locating and/or processing embedded foods such as underground roots and insects or hard-shelled nuts and fruits. It is shown that, although only cebus monkeys and chimpanzees in the wild use tools in extractive foraging, many other species of mammals (including primates) and birds are capable of extracting embedded foods without tools. Extractive foraging by primates is compared to extractive foraging by other mammals and birds to assess whether: 1) extractive foraging involves cognition, and 2) extractive foraging by primates is unique in a way that may mean it played a role in the development of intelligence among primates. This comparison reveals that some acts of extractive foraging by nonprimates are equally sophisticated as those of primates. It is suggested that extractive foraging played no significant role in the evolution of primate intelligence. Hypotheses for testing precise differences in extractive foraging ability across taxa are offered, and the roles of olfactory cues, manual dexterity, and strength in extractive foraging are evaluated. In conclusion, the hominization process is briefly reviewed in relation to foraging behavior. A ?package? of traits that, in combination, is unique to hominids is discussed: tool-aided extractive foraging, division of labor by sex with food exchange, and feeding of juveniles.     

Studies of primate protein variation and evolution: Microelectrophoretic detection

Genetic variation at 16 protein and enzyme loci in Cercopithecus aethiops and several other primate species has been surveyed, using cellulose acetate microelectrophoresis. Resolution of several standard variant proteins is comparable to that achieved on starch gel or polyacrylamide gel. Although both intraspecific and interspecific variation was observed for some loci, the data generally support the concept that extracellular proteins are more likely to be polymorphic within a species, while intracellular proteins generally vary between species, if at all. These methodologies are particularly appropriate for screening multiple-locus variation in large numbers of samples; their relevance to studies of molecular evolution and evaluation of theories of kin selection is discussed.This research was supported in part by California State Agricultural Experiment Station Funds to the University of California, Berkeley, and the Wenner Gren Foundation.     

Leopard predation and primate evolution

Although predation is an important driving force of natural selection its effects on primate evolution are still not well understood, mainly because little is known about the hunting behaviour of the primates' various predators. Here, we present data on the hunting behaviour of the leopard (Panthera pardus), a major primate predator in the Tai; forest of Ivory Coast and elsewhere. Radio-tracking data showed that forest leopards primarily hunt for monkeys on the ground during the day. Faecal analyses confirmed that primates accounted for a large proportion of the leopards' diet and revealed in detail the predation pressure exerted on the eight different monkey and one chimpanzee species. We related the species-specific predation rates to various morphological, behavioural and demographic traits that are usually considered adaptations to predation (body size, group size, group composition, reproductive behaviour, and use of forest strata). Leopard predation was most reliably associated with density, suggesting that leopards hunt primates according to abundance. Contrary to predictions, leopard predation rates were not negatively, but positively, related to body size, group size and the number of males per group, suggesting that predation by leopards did not drive the evolution of these traits in the predicted way. We discuss these findings in light of some recent experimental data and suggest that the principal effect of leopard predation has been on primates' cognitive evolution.     

Cranial morphology and development: new light on the evolution of language

A hypothesis is presented which may explain within a single framework both the large behavioural differences and the large differences in head morphology between the great apes and humans. All these differences can be parsimoniously explained by a shift of few regulatory genes controlling the onset of the division of late migrating neurons in the human cortex. This simple shift resulted in the following effects: 1) the neurocranium responded to brain enlargement by increasing mineral deposition on its external surface, increasing its overall size and mass. 2) This increase in the braincase was largely achieved by developmental reabsoption of the face bones. 3) The relative shift in growth between these two skull components also induced a rearrangement at the basicranium level. This brought about the facial orthognatism of modernHomo and, as a mechanical by-product, the descent of the larynx into the throat. Brain enlargement led to a large increase in cognitive capacity, and as a developmental byproduct, produced a mechanical organ preadapted for speech, as well as bringing about the reduction of canines and the origin of the chin. In this study, the phylogenetic basis, the selective pressures, and the behavioural consequences of this process during hominization are examined. Cognitiveversus communicative aspects of human language are distinguished and discussed. Cognitive capacities were the first to be selected due to the survival advantage of mapping huge territories during the expansion of the Plio-Pleistocene savanna ecotone. The present hypothesis is then compared with current theories leading to the conclusion that it is a more parsimonious explanation. It integrates data from a wide array of fields of human biology, pathology and clinical medicine, all assessed from evolutionary and ecological perspectives.     

Origin and evolution of primate social organisation: a reconstruction

The evolution and origin of primate social organisation has attracted the attention of many researchers, and a solitary pattern, believed to be present in most nocturnal prosimians, has been generally considered as the most primitive system. Nocturnal prosimians are in fact mostly seen alone during their nightly activities and therefore termed 'solitary foragers', but that does not mean that they are not social. Moreover, designating their social organisation as 'solitary', implies that their way of life is uniform in all species. It has, however, emerged over the last decades that all of them exhibit not only some kind of social network but also that those networks differ among species. There is a need to classify these social networks in the same manner as with group-living (gregarious) animals if we wish to link up the different forms of primate social organisation with ecological, morphological or phylogenetic variables. In this review, we establish a basic classification based on spatial relations and sociality in order to describe and cope properly with the social organisation patterns of the different species of nocturnal prosimians and other mammals that do not forage in cohesive groups. In attempting to trace the ancestral pattern of primate social organisation, the Malagasy mouse and dwarf lemurs and the Afro-Asian bushbabies and lorises are of special interest because they are thought to approach the ancestral conditions most closely. These species have generally been believed to exhibit a dispersed harem system as their pattern of social organisation ('dispersed' means that individuals forage solitarily but exhibit a social network). Therefore, the ancestral pattern of primate social organisation was inferred to be a dispersed harem. In fact, new field data on cheirogaleids combined with a review of patterns of social organisation in strepsirhines (lemurs, bushbabies and lorises) revealed that they exhibit either dispersed multi-male systems or dispersed monogamy rather than a dispersed harem system. Therefore, the concept of a dispersed harem system as the ancestral condition of primate social organisation can no longer be supported. In combination with data on social organisation patterns in 'primitive' placentals and marsupials, and in monotremes, it is in fact most probable that promiscuity is the ancestral pattern for mammalian social organisation. Subsequently, a dispersed multi-male system derived from promiscuity should be regarded as the ancestral condition for primates. We further suggest that the gregarious patterns of social organisation in Aotus and Avahi, and the dispersed form in Tarsius evolved from the gregarious patterns of diurnal primates rather than from the dispersed nocturnal type. It is consequently proposed that, in addition to Aotus and Tarsius, Avahi is also secondarily nocturnal.     

Sleeping site ecology in a rain-forest dwelling nocturnal lemur (Lepilemur mustelinus): implications for sociality and conservation

Suitable sleeping sites as potentially restricted resources are suggested to shape sociality in primates. We investigated sleeping site ecology of a rain-forest dwelling sportive lemur in eastern Madagascar for the first time. Using radiotelemetry, we characterized the type, quality and usage of sleeping sites as well as social sleeping habits of 11 focal individuals of the weasel sportive lemur (Lepilemur mustelinus) during the dry and the onset of the rainy season. Morphometric measurements provided additional information. The sexes showed an unusual sexual dimorphism for primates. Males and females did not differ in body length, but females surpassed males in body mass suggesting female dominance. Both sexes used dense vegetation and holes in hollow trees high above the ground as shelters for sleeping during the day. No sex difference in the quality of tree holes was found, but focal individuals used tree holes more often than open sleeping sites in dense vegetation. Both sexes showed high sleeping site fidelity limited to two to six different sites that they used primarily solitarily. The results imply that suitable sleeping sites are limited and survival of this species will strongly depend on the availability of mature rain forests with suitable hollow trees. Furthermore, these findings provide evidence of a solitary sleeping and ranging system in this rain-forest dwelling sportive lemur with suitable sleeping sites as defendable resources.     

The evolution of primate communities and societies in Madagascar

During their 120 to 165 million years of isolation, the flora and fauna of Madagascar evolved, to a large extent, independently of the African mainland.¹ In contrast to other oceanic islands, Madagascar is large enough to house the major components of tropical ecosystems, allowing tests of evolutionary hypotheses on the level of complete communities. Taking lemurs, the primates of Madagascar, as an example, evolutionary hypotheses correctly predict the organization of their community structure with respect to ecological correlates. Lemur social systems and their morphological correlates, on the other hand, deviate in some respects from those of other primates. Apparently, lemur social systems are influenced by several selection pressures that are weak or rare in other primates. These include variable activity patterns and avoidance of infanticide. The interspecific variation in lemur social systems therefore offers a unique opportunity for a comprehensive study of the determinants of primate social systems.     

Signaling,solidarity, and the sacred: The evolution of religious behavior

Anthropologists have repeatedly noted that there has been little theoretical progress in the anthropology of religion over the past fifty years.^1–7 By the 1960s, Geertz² had pronounced the field dead. Recently, however, evolutionary researchers have turned their attention toward understanding the selective pressures that have shaped the human capacity for religious thoughts and behaviors, and appear to be resurrecting this long‐dormant but important area of research.^8–19 This work, which focuses on ultimate evolutionary explanations, is being complemented by advances in neuropsychology and a growing interest among neuroscientists in how ritual, trance, meditation, and other altered states affect brain functioning and development.^20–26 This latter research is providing critical insights into the evolution of the proximate mechanisms responsible for religious behavior. Here we review these literatures and examine both the proximate mechanisms and ultimate evolutionary processes essential for developing a comprehensive evolutionary explanation of religion.     

The adaptive legacy of human evolution: A search for the environment of evolutionary adaptedness

The growth of evolutionary psychology has led to renewed interest in what might be the significant evolutionary heritage of people living today, and in the extent to which humans are suited to a particular adaptive environment—the EEA. The EEA, though, is a new tool in the battery of evolutionary concepts, and it is important both that it is scrutinized for its utility, and that the actual reconstructions of the environments in which humans and hominids evolved are based on sound palaeobiological inference and an appropriate use of the phylogenetic context of primate evolution.     

Out of Africa and the evolution of human behavior

Twenty‐one years ago, a landmark exploration of mitochondrial DNA diversity popularized the idea of a recent African origin for all living humans. 1 The ancestral African population was estimated to have existed 200 ka (thousands of years ago) plus or minus a few tens of thousands of years. A corollary was that at some later date the fully modern African descendants of that population expanded to swamp or replace the Neanderthals and other nonmodern Eurasians. The basic concept soon became known as “Out of Africa,” after the Academy Award winning film (1985) that took its title, in turn, from Isak Dinesen's classic autobiography (1937). Many subsequent genetic analyses, including those of Ingman and coworkers 2 and Underhill and coworkers, 3 have reaffirmed the fundamental Out of Africa model. The fossil and archeological records also support it strongly. The fossil record implies that anatomically modern or near‐modern humans were present in Africa by 150 ka; the fossil and archeological records together indicate that modern Africans expanded to Eurasia beginning about 50 ka.     

From action to language: comparative perspectives on primate tool use, gesture and the evolution of human language

The papers in this Special Issue examine tool use and manual gestures in primates as a window on the evolution of the human capacity for language. Neurophysiological research has supported the hypothesis of a close association between some aspects of human action organization and of language representation, in both phonology and semantics. Tool use provides an excellent experimental context to investigate analogies between action organization and linguistic syntax. Contributors report and contextualize experimental evidence from monkeys, great apes, humans and fossil hominins, and consider the nature and the extent of overlaps between the neural representations of tool use, manual gestures and linguistic processes.     

Niche construction,human behavior,and the adaptive‐lag hypothesis

Niche construction is the process whereby organisms modify selective environments, thereby affecting evolution. The niche‐construction perspective is particularly relevant to researchers using evolutionary methods to interpret human behavior and society. On the basis of niche‐construction theory, we argue against the hypothesis that modern humans experience an atypically large adaptive lag. We stress that humans construct their world largely to suit themselves and frequently buffer adaptive lag through cultural niche construction. Where they are unable to do that, natural selection of genes rapidly ensues. Our argument has implications for evolutionary psychology and human behavioral ecology, and suggests that the methods of the latter are potentially applicable to all human societies, even postindustrial ones.     

Introduction. Cultural transmission and the evolution of human behaviour

The articles in this theme issue seek to understand the evolutionary bases of social learning and the consequences of cultural transmission for the evolution of human behaviour. In this introductory article, we provide a summary of these articles (seven articles on the experimental exploration of cultural transmission and three articles on the role of gene-culture coevolution in shaping human behaviour) and a personal view of some promising lines of development suggested by the work summarized here.     

Pair-specific usage of sleeping sites and their implications for social organization in a nocturnal Malagasy primate, the Milne Edwards' sportive lemur (Lepilemur edwardsi)

Safe sleeping sites may be a limited resource crucial for survival. In order to investigate their potential significance for social organization in nocturnal primates, we analyzed the spatial distribution of daily sleeping sites, their characteristics, their usage, and sleeping group compositions in the nocturnal Milne Edwards' sportive lemur during a 6-month field study in the dry deciduous forest of northwestern Madagascar. Sexes did not differ either in body size or in body mass. Sleeping sites were used almost exclusively by adult male-female pairs. Individuals showed a high sleeping-site fidelity limited to 2-3 different sleeping sites in close vicinity during the whole study period. Most females showed a higher fidelity to one distinct sleeping site than their male partners. Sleeping groups consisted of one adult male and one adult female and remained stable in composition over the whole study period. Exclusive pair-specific usage of sleeping sites suggests sleeping site related territoriality of male-female pairs, perhaps influenced by inter- and intrasexual resource competition. Results give first insights into the distribution patterns and social organization of this species. They imply dispersed monogamy for the Milne Edwards' sportive lemur, with sleeping sites as a potentially restricted and defendable resource.     

A new research strategy for integrating studies of paleoclimate,paleoenvironment, and paleoanthropology

Paleoanthropologists (scientists studying human origins) universally recognize the evolutionary significance of ancient climates and environments for understanding human origins. 1 - 6 Even those scientists working in recent phases of human evolution, when modern humans evolved, agree that hunter‐gatherer adaptations are tied to the way that climate and environment shape the food and technological resource base. 7 - 10 The result is a long tradition of paleoanthropologists engaging with climate and environmental scientists in an effort to understand if and how hominin bio‐behavioral evolution responded to climate and environmental change. Despite this unusual consonance, the anticipated rewards of this synergy are unrealized and, in our opinion, will not reach potential until there are some fundamental changes in the way the research model is constructed. Discovering the relation between climate and environmental change to human origins must be grounded in a theoretical framework and a causal understanding of the connection between climate, environment, resource patterning, behavior, and morphology, then move beyond the strict correlative research that continues to dominate the field.     

Uplift of the roof of africa and its bearing on the evolution of mankind

Evidence concerning the geomorphological evolution of the Western Rift Valley, sedimentation within the valley and comparison of the fossil mammalian faunas of Western Uganda and East Africa indicate that the mountain ranges which now flank the Western Rift were uplifted in three or more stages beginning during the upper Miocene and that they reached climatically important altitudes during the upper Pliocene, at which time they began to modify regional climatic patterns in East Africa. Their main effect was the xerification of conditions over much of the region east of the mountains. The regional climatic effects due to the mountain ranges were themselves modified by global climatic changes related to the onset of the Glacial Period, the two phenomena combining to yield the Present day climatic regime of East Africa. As the climate changed, so did the flora and fauna. Faunal response was of three main kinds: a) dispersal into East Africa of pre-existing forms already adapted to more xeric conditions (many bovids, some cercopithecids), b) autochthonous evolution of forms adapted to mesic environments into forms adapted to more xeric conditions (suids, elephantids, some bovids, hominids), c) displacement of species ranges of those lineages unable to adapt to changing conditions (i.e. local extinctions) (Anancus, Brachypotherium). Autochthonous evolvers, including hominids, adopted two main strategies reflected in their hard anatomy: a) dietary shift (suids, proboscideans, bovids and later Pliocene hominids) and b) locomotor changes (early Pliocene hominids).     

Anthropo-entomophagy: Cultures, evolution and sustainability

Environmental cycles and human factors have altered ecosystems throughout the world. Natural resources have acquired high value because they are important to life and the survival of human beings. Among these resources are edible insects. They have many important features and, to date, up to 2086 species are consumed by 3071 ethnic groups. Rural people, who primarily search, gather, fix, commercialize and store this important natural resource, do not exterminate them. This is because rural people exploit only the central part of the insects' population curves. Nonetheless, some species are overexploited. Anthropo-entomophagy (eating of insects by humans) constitutes a major source of nutrition and these foods are eaten in 130 countries, with the African and American continents being the most entomophagous until now. It exists in protocultures (care is given to the edible insect species) and formal cultures, such as in Mexico, which date back to prehisphanic times. According to anthropologists the "saving gene theory" is based on insect ingestion, which, since the Paleolithic era, has given human beings reproductive success. The evolution of anthropo-entomophagy has been achieved in many ways, from the point of view of collection, fixing, marketing and consumption, and for the insects' organoleptical qualities. The sustainability of these species is fundamental; therefore, it is necessary to take certain measures for species conservation. In Mexico, more than 100 species of edible insects have been tested for their sustainability over 500 years, from the Spanish conquest to the present.     

Mating games: the evolution of human mating transactions

We propose a new, evolutionary, game-theoretic model of conditionalhuman mating strategies that integrates currently disconnectedbodies of data into a single mathematically-explicit theoryof human mating transactions. The model focuses on the problemof how much resource a male must provide to a female to secureand retain her as a mate. By using bidding-game models, we showhow the male's minimally required resource incentive variesas a function of his own mate value, the value of the female,and the distribution of the mate values of their available alternativemates. The resulting theory parsimoniously accounts for strategicpluralism within the sexes, mate choice differences betweenthe sexes, and assortative mating, while generating a rich setof testable new predictions about human mating behavior.