1 1(MRC Unit on the Development and Integration of Behaviour, Cambridge University, Madingley, Cambridge, U.K., Departamento de Psicologia Evolutiva, Universidad Autónoma de Madrid, 28049 Madrid, Spain
Matrilineal structures are typical of many species of Old World monkeys including the savanna baboon. Both isosexual dyads of females and heterosexual dyads frequently reach the stage of greatest social compatibility, i.e. grooming. Male dyads, in contrast, very rarely reach such stage, they show instead marked mutual intolerance and overt aggressive competition. Grooming and other forms of physical contact are fairly frequent between adult males in the patrilineal society of chimpanzees. In the hamadryas baboon, also with patrilineal organization, adult males do not groom with each other but they frequently exchange greeting interactions, particularly in contexts of excitement provoked by social tension. Species-specific differences (savanna versus desert baboons) in the morphology of greeting interactions have also been reported. The objective of this study was to examine the nature and function of this category of non-agonistic interactions recorded over a period of 9 years between 20 males members of a well-established colony of baboons, Papio hamadryas, P. cynocephaus and their hybrids, housed in a large, open enclosure in the Madrid Zoo. Greetings were conceptualized as interactions, i.e. in which each participant's action is examined in relation to that of the other interacting partner. A description and qualitative analysis were provided of the morphology (i.e. facial, vocal, manipulatory and contact, postural and orientation, and locomotory patterns) and properties (i.e. reciprocity/non-reciprocity, and symmetry/asymmetry) of greeting interactions. The most significant feature of greeting interactions was the three-stage pattern of performance observed, corresponding with the phases of approximation, proximity, and retreat. In each phase, characteristic behavioural patterns were displayed, some were quite stereotyped but others seemed to be rather influenced by the identity of, and social relationship of, the interacting males, and also by the immediate social context of the interaction. A quantitative analysis of 1583 greeting interactions and 1039 aggressive episodes between the 20 study males was then carried out. Individual males were assigned to one of the following classes of reproductive status: subadult (SA), follower (FW), new leader (NL), prime leader (PL), old leader (OL), and old follower (OFW). It was found a correlation between a male's status class and the frequency with which he played several different roles in greeting and aggressive interactions. Greeting interactions were typical of mature males (FWs, NLs, PLs, OLs, and OFWs), but very especially of reproductive males (NLs, PLs, and OLs). Their rate of participation (both as initiator and recipient) was positively related both to the size of their harem (e.g. prime leaders) and to the potentiality to increase the harem size by taking over new females (e.g. prime and new leaders). Males at its prime reproductive period (i.e. PLs) showed the highest rates of involvement in symmetrical greetings, and the males who were reaching that stage (i.e. NLs) were the ones who most frequently refused to reciprocate a greeting approach. As males approached the stages of higher reproductive potential their rates of symmetrical, i.e. non-contact and notifying, greetings increased. In contrast, the contact patterns observed during asymmetrical greetings were mostly displayed in interactions in which at least one of the participants was either an immature or a young nonreproductive (i.e. follower) male. Reproductive males, i.e. prime and new leaders, were the most frequent initiators and recipients of both greeting and aggression. Examination of the morphology of greeting interactions, particularly of the symmetrical and unreciprocated greetings, i.e. the approach/retreat non-contact pattern, that were typical of prime and new leader males, and of the contexts in which both aggression and many greeting episodes took place, i.e. agonistic conflicts and competition over resources, suggested that these two categories of behaviour might share some causal factors and that they might be regarded as two alternative strategies to deal with a similar problem, namely, the resolution of conflicts. In many cases, greeting may be regarded as a quasi-aggressive behaviour aimed at testing a potential or actual rival's tendencies in a competition situation rather than as a category of affiliative or friendly behaviour. Greeting in baboons is a nice example of a non-stereotyped behaviour in a higher animal, in which relational and interactional properties can be studied, and in which, as discussed in the paper, all the traditional ethological issues of causation, development, function, and evolution can be addressed.