Louise Barrett

Market forces predict grooming reciprocity in female baboons

We argue that grooming is a commodity that female primates can trade, either for itself or in exchange for other services (sensu biological markets theory) and that the decision to do either will depend on the degree of competition within a social group. We test this using data from four chacma baboon troops, living in two populations that differ markedly in the degree of contest competition. As predicted by the predominance of grooming dyads in which females are closely ranked there was, in all four troops, a positive correlation between the time invested by one partner and that by the other. In addition, as predicted, the allocation of time was more closely matched in troops where grooming could not be exchanged for anything else. In troops where resource competition was high, we found in one of two troops a positive relationship between rank distance and the discrepancy in time allocation, with the lower ranking of the partners contributing more grooming.

Infants as a commodity in a baboon market

We used data from adult female chacma baboons, Papio cynocephalus ursinus, to provide the first test of hypotheses on interchange trading and the structure of a biological market (Noe ¨ & Hammerstein 1994, Behavioral Ecology and Sociobiology, 35, 1–11) within a primate group. The interchange commodities selected were grooming and handling of infants less than 3 months of age. Patterns of grooming in relation to infant handling showed strong evidence for interchange. Grooming for infant access was initiated by potential handlers and was significantly likely to be nonreciprocated. More critically, the data show that infant ‘supply’ created a market effect: grooming bout duration (the price ‘paid’ for handling) was inversely related to the number of infants present in the group. In addition, there was an inverse relationship between grooming bout duration and the rank distance between mothers and handlers, suggesting that higher-ranking mothers could demand a higher price for infant handling. Where rank distance was high, females were able to handle infants without grooming. Dominance could thus be used to disrupt the infant market effect. If biological markets models are to be fully applicable to primate groups (and those of other social mammals) then the potentially distorting effect of dominance needs to be incorporated into the framework.

Social brains, simple minds: does social complexity really require cognitive complexity?

The social brain hypothesis is a well-accepted and well-supported evolutionary theory of enlarged brain size in the non-human primates. Nevertheless, it tends to emphasize an anthropocentric view of social life and cognition. This often leads to confusion between ultimate and proximate mechanisms, and an over-reliance on a Cartesian, narratively structured view of the mind and social life, which in turn lead to views of social complexity that are congenial to our views of ourselves, rather than necessarily representative of primate social worlds. In this paper, we argue for greater attention to embodied and distributed theories of cognition, which get us away from current fixations on ‘theory of mind’ and other high-level anthropocentric constructions, and allow for the generation of testable hypotheses that combine neurobiology, psychology and behaviour in a mutually reinforcing manner.

Cyclicity in the structure of female baboon social networks

There is an established and very influential view that primate societies have identifiable, persistent social organizations. It assumes that association patterns reflect long-term strategic interests that are not qualitatively perturbed by short-term environmental variability. We used data from two baboon troops in markedly different habitats over three consecutive seasons to test this assumption. Our results demonstrate pronounced cyclicity in the extent to which females maintained differentiated relationships. When food was plentiful, the companionships identified by social network analysis in the food-scarce season disappeared and were replaced by casual acquaintanceships more representative of mere gregariousness. Data from the fourth, food-scarce, season at one site indicated that few companions were re-united. It is likely that this reflected stochastic variation in individual circumstances. These results suggest that attention could profitably be paid to the effects of short-term local contingencies on social dynamics, and has implications for current theories of primate cognitive evolution.

The social nature of primate cognition

The hypothesis that the enlarged brain size of the primates was selected for by social, rather than purely ecological, factors has been strongly influential in studies of primate cognition and behaviour over the past two decades. However, the Machiavellian intelligence hypothesis, also known as the social brain hypothesis, tends to emphasize certain traits and behaviours, like exploitation and deception, at the expense of others, such as tolerance and behavioural coordination, and therefore presents only one view of how social life may shape cognition. This review outlines work from other relevant disciplines, including evolutionary economics, cognitive science and neurophysiology, to illustrate how these can be used to build a more general theoretical framework, incorporating notions of embodied and distributed cognition, in which to situate questions concerning the evolution of primate social cognition.

Constraints and flexibility in mammalian social behaviour: introduction and synthesis

This paper introduces a Theme Issue presenting the latest developments in research on the interplay between flexibility and constraint in social behaviour, using comparative datasets, long-term field studies and experimental data from both field and laboratory studies of mammals. We first explain our focus on mammals and outline the main components of their social systems, focusing on variation within- and among-species in numerous aspects of social organization, mating system and social structure. We then review the current state of primarily ultimate explanations of this diversity in social behaviour. We approach the question of how and why the balance between behavioural flexibility and continuity is achieved by discussing the genetic, developmental, ecological and social constraints on hypothetically unlimited behavioural flexibility. We introduce the other contributions to this Theme Issue against this background and conclude that constraints are often crucial to the evolution and expression of behavioural flexibility. In exploring these issues, the enduring relevance of Tinbergens seminal paper ‘On aims and methods in ethology’, with its advocacy of an integrative, four-pronged approach to studying behaviour becomes apparent: an exceptionally fitting tribute on the 50th anniversary of its publication.

Day length, latitude and behavioural (in)flexibility in baboons (Papio cynocephalus ursinus)

Annual cycles in day length are an important consideration in any analysis of seasonal behaviour patterns, since they determine the period within which obligate diurnal or nocturnal animals must conduct all of their essential activities. As a consequence, seasonal variation in day length may represent an ecological constraint on behaviour, since short winter days restrict the length of the time available for foraging in diurnal species (with long summer days, and thus short nights, a potential constraint for nocturnal species). This paper examines monthly variation in activity patterns over a 4-year study of chacma baboons (Papio cynocephalus ursinus) at De Hoop Nature Reserve, South Africa. Time spent feeding, moving, grooming and resting are all significant positive functions of day length, even before chance events such as disease epidemics and climatically mediated home range shifts have been accounted for. These results provide strong support for the idea that day length acts as an ecological constraint by limiting the number of daylight hours and thus restricting the active period at certain times of year. Day length variation also has important implications across populations. Interpopulation variation in resting time, and non-foraging activity in general, is a positive function of latitude, with long summer days at temperate latitudes apparently producing an excess of time that cannot profitably be devoted to additional foraging or social activity. However, it is the short winter days that are probably of greatest importance, since diurnal animals must still fulfil their foraging requirements despite the restricted number of daylight hours and elevated thermoregulatory requirements at this time of year. Ultimately this serves to restrict the maximum ecologically tolerable group sizes of baboon populations with increasing distance from the equator. Seasonal variation in day length is thus an important ecological constraint on animal behaviour that has important implications both within and between populations, and future studies at non-equatorial latitudes must clearly be mindful of its importance.

Taking sociality seriously: the structure of multi-dimensional social networks as a source of information for individuals

Understanding human cognitive evolution, and that of the other primates, means taking sociality very seriously. For humans, this requires the recognition of the sociocultural and historical means by which human minds and selves are constructed, and how this gives rise to the reflexivity and ability to respond to novelty that characterize our species. For other, non-linguistic, primates we can answer some interesting questions by viewing social life as a feedback process, drawing on cybernetics and systems approaches and using social network neo-theory to test these ideas. Specifically, we show how social networks can be formalized as multi-dimensional objects, and use entropy measures to assess how networks respond to perturbation. We use simulations and natural ‘knock-outs’ in a free-ranging baboon troop to demonstrate that changes in interactions after social perturbations lead to a more certain social network, in which the outcomes of interactions are easier for members to predict. This new formalization of social networks provides a framework within which to predict network dynamics and evolution, helps us highlight how human and non-human social networks differ and has implications for theories of cognitive evolution.

MALE CONSORTSHIP BEHAVIOUR IN CHACMA BABOONS: THE ROLE OF DEMOGRAPHIC FACTORS AND FEMALE CONCEPTIVE PROBABILITIES

There is evidence for a general relationship between male dominance rank and mating success in primates, although the strength of this relationship differs among species. In chacma baboons (Papio hamadryas ursinus) male rank is found to be of more importance than in the other savannah baboon subspecies. However, even though the priority-of-access model explains the proportion of time spent in consortship for males of different rank in chacmas, highest-ranking males usually consort less often than expected. In this study, conducted in the Drakensberg Mountains of Natal and at De Hoop in the Western Cape, we investigated why dominant males in four study troops consorted only between 50% and 75% of days that they were expected to consort according to the priority-of-access model. Consortship success of highest-ranking males was primarily dependant on the number of available oestrous females in a troop. This was likely due to costs involved in consorting which limit the amount of days that a male could spend in consortship. Females pass through several cycles before conceiving and highest-ranking males were observed to consort more often on the conceptive cycle compared to the nearest nonconceptive cycle, but this was only true for males that were already resident for several months. Recently immigrated males that became highest-ranking often consorted during nonconceptive female cycles, while older, lower-ranking males consorted during the conceptive cycles. We propose that males with longer residency have more information about reproductive state of females and thus higher reproductive success than recently immigrated males.

Maternal investment in mountain baboons and the hypothesis of reduced care

Abstract It has been argued that female mammals should terminate expensive forms of infant care earlier as habitat quality declines. More recently it has been shown that among a variety of mammalian species, early termination of care is also associated with highly favourable conditions. In this paper we present data on maternal investment decisions among baboons (Papio cynocephalus ursinus) inhabiting the Drakensberg Mountains of South Africa, and compare these with data from East African baboon studies. Mothers in the mountain habitat face a set of environmental conditions where the problem of resource allocation to offspring is expected to be particularly acute. We begin by using the model of Altmann (1980) of maternal time budgets to demonstrate that mountain baboon mothers experience greater perturbations to their activity budgets while suckling than do mothers in other populations. They also provide consistently greater levels of care to their infants and do so in the absence of any form of overt conflict over access to the nipple. Although this investment results in a relative lengthening of the interbirth interval (IBI), it is accompanied by relatively higher infant survival. We argue that factors that influence the maternal strategy adopted by mountain baboons include slow infant growth rates and a lack of predation in the habitat which influences probability of offspring survival beyond the immediate postnatal period. We suggest that both “care-dependent” sources of mortality (e.g. female reproductive condition, the amount of milk transferred to offspring) as well as “care independent” sources of mortality (e.g. predation, infectious disease) should be considered in studies of parental investment.