Marriage and monkey business

As Hans Kummer tells it, the route to his study of the wild hamadryas baboons of Ethiopia began with a chance opportunity to do his postgraduate research on a group of them in Zurich Zoo.

He was an exceptionally lucky man because hamadryas society proved to be intrinsically fascinating, with undreamt-of levels of structural complexity, and a system of "marriage" (multiple stable pair-bonds coexisting in a single group) found only in our own and two other primate species.

Between 1961 and 1977 (when the war with Somalia closed the project), Kummer and his team eventually distinguished four levels of social structure. At the lowest level is the "family", in which a single adult male fiercely guards a small harem of females and their offspring. Several families form a "clan", typically moving and feeding together. That clan males are close kin is often evident merely by close inspection of their faces - there is the violet clan, the red clan, and so on. The "band" is made up of several clans that form a looser daily foraging party, meeting at intervals, notably at critically important water holes. Finally, bands converge temporarily into "troops" that may number more than 100 to exploit the safety of limited sleeping cliffs. This fission-fusion society can "unzip" between each of the four levels to exploit different resource patterns as the occasion permits.

In all these respects, hamadryas baboons are quite different even from the several species of savannah baboons that other primatologists have studied across the remainder of sub-Saharan Africa. Their unique behaviours have entranced a generation (or two) of ethologists, but the discoveries of Kummer and his students have also had a wider impact on our understanding of principles of social dynamics in complex groups.

It takes a very special scientist to extract the underlying order from the turmoil of social interchange that swirls on the surface of primate troops such as those of the hamadryas. Kummer has that gift in good measure, and in this book he encourages the reader to share his journey of discovery. The writing is crisp, clear and engaging, adjectives that also characterise the scientific detective story which Kummer tells. Although most of the research was done more than 20 years ago, budding primatologists would do well to assimilate its lessons, while non-primatologists will find here an absorbing account of how a master field primatologist operates. Kummer is at great pains to use the book to describe all those aspects of doing scientific field research left out of the string of learned papers that typically chart a long-term primate study. He vividly describes the moulding of his ideas, from critical observations that offered insights to someone prepared to see them for what they were, to camp fire musings on the ins and outs of the latest theoretical puzzle to engage him. The science of Hamadryas society is interspersed with colourful accounts of day-by-day dramas of life in the field, among the desert peoples with whom Kummer and his family had both affectionate and at times quite violent dealings.

Much of Kummer's early interpretation of social dynamics had a group-selection flavour to it. In part this was simply the spirit of the age, preceding the sociobiological revolution of the 1970s. But we also hear that Kummer's earliest training was in developmental biology, with a focus on the way component parts of embryos communicate and cooperate to build the whole organism - an image that appears to have coloured his thinking about the social unit (family, clan and so on) as an organism, with its hierarchically organised components working for its greater good. In this volume Kummer re-evaluates earlier findings in the light of today's sociobiological predictions, finding in favour of the latter. For example, the inhibition of adult males in the face of an already existing bond between a desirable female and another male is now seen as an individually optimal response, rather than representing a functionally moral contribution to the cohesion of the clan.

A particular flair of the hamadryas project was in the use of sometimes quite dramatic field experiments to test hypotheses arising from observations of spontaneous behaviour. Kummer remarks that these too can be traced to his early embryological training, in which developing organs are experimentally transplanted. Seeking to tease apart the roles of inheritance and experience in the formation of sexual strategies, Kummer and his team therefore captured individual savannah baboons and released them into hamadryas groups, with hamadryas females released in a similar fashion as controls. The male hamadryas attempted to herd the females, harassing and biting them if they strayed too far. With transplanted females of their own species this results in the usual coherent harems of closely attached females. The savannah females also learned initially to avoid harassment by staying by the male, a habit not seen in savannah baboon society. In the longer term, however, the male could not sustain the degree of herding required and the females became more mobile and independent, as they are in groups of their own species. The results of experiments like these, together with the behaviour of baboons at the natural border between the species, suggest a limited capacity to learn the habits of the sister species and a strong tendency to revert to species-specific mating norms for both males and females.

In the later phases of the project, attention widened from social dynamics to the exploitation of the physical environment and further ground-breaking findings emerged, like those concerning the baboons' mental map, social negotiation over route-making, and individual differences in social versus foraging expertise. As the project matured, important insights into development at individual and social levels began to accumulate. It is tragic that such a productive research programme was cut short by the habitual folies of the primate who wages war, but Kummer's book is an inspiring record of its achievements.

Andrew Whiten is reader in psychology, University of St Andrews.