A recent survey informs us that while biologists generally tend to be men, most primatologists are women. Louis Leakey pronounced women as better observers of primates, but perhaps it is just a certain kind of woman who has the staying power primatology requires. Two women at the top of their fields tell very different tales.

The publication of Reflections of Eden completes the ape trilogy begun with Jane Goodall's chimps and Diane Fossey's gorillas and, on many bookshelves, will be comfortably slotted in next to In the Shadow of Man and Gorillas in the Mist. Galdikas was the third of Leakey's "ape women" dispatched on tenuous missions around the world to create a living model of human ancestry to complement Leakey's fossil work. Inevitably this work and Galdikas herself will be compared with their predecessors.

While the book contains very little in the way of data, Galdikas has nevertheless produced a fine piece of writing. The Eden of the title is the tropical rainforest of our ancestry and the author very evocatively communicates its sinister dual aspect: the abundance of life carrying with it the oppressive certainty of death and decay.

While the diminutive Galdikas seems at times dwarfed by her surroundings, by her undertaking she is not. Galdikas unashamedly declares that she was born to study orangutans and that her life's work is no more than the achievement of her destiny, thus there is little here to dilute the Fossey stereotype of grim determination winning the day: the enduring presence of Camp Leakey (Galdikas's original field station) testifies to this as much as the various exploits reported in her book. These exploits make entertaining reading and assure the success of the book among a popular readership: Galdikas and husband, subsisting on the fieldworker's staple fare of rice and sardines, endure not only leeches, fire ants and the like, but also the ignominy of being defecated on from above by their study subjects.

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Orangutans assume three faces in this book. The first is that of the individuals Galdikas finds free-ranging in the forest; their personalities and the events that characterise their lives - and deaths. Galdikas recreates the excitement of discovering not only each animal but also uncovering the most essential aspects of orangutan behaviour- though such an arid term as behaviour does not really seem to do justice to what is recounted. She is actively anthropomorphic and yet the species seems to deserve it.

Interwoven with this narrative is another concerning the (seemingly unintended) growth of Camp Leakey as a rehabilitation centre for ex-captive orangutans. The author finds herself the adopted mother of a clutch of babies, none of them house-trained and all of them tenacious, jealous and exploitative of their hapless provider's softheartedness. The average fieldworker is entitled to put his or her feet up at the end of the day and forget about the animals but this is difficult when your study subjects are in the rafters disembowelling pillows or in the kitchen attempting to make pancakes.

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The third face that we see is the retrospective understanding of the species that can only come through a long-term field study, and it is through the efforts of Galdikas and fieldworkers elsewhere in Indonesia that we are at last able to judge the orangutan fairly on its own ground. In fact, the orangutan may prove to be the most extraordinary of the great apes. The ascendant theory concerning primate and hominid intelligence is that it evolved to meet the complexities of social life, either in cooperative or exploitative, Machiavellian contexts. Orangutans are an embarrassment for this theory, since despite impressive intellectual credentials they spend 98 per cent of their time alone. Certainly the few interactions Galdikas witnesses (typically sexual ones) are artfully depicted as subtle, complex events, the details of which the subjects will remember for their lifetime. But for the most part, orangutans are characterised by Galdikas as self-contained animals for whom eating comes before socialising: a distinct contrast with the more gregarious, and more political chimpanzee.

In consequence, their intellect is geared towards knowing what to eat and where to find it. Orangutans eat more than 400 food types, each of which presents special problems in location and processing and it is only through being superb botanists that orangutans can fill their stomachs It is not hard to starve to death in Eden as the hapless soldiers of the British Army, reduced to a ration of half a Polo mint a day, recently came close to discovering.

This is not to say that the intelligence of orangutans cannot be used for generalised purposes. It is around Camp Leakey and its human paraphernalia that the intellect of orangutans really comes into its own, for it is there that rehabilitant animals show their remarkable capacity for imitation - this going so far as stealing and using boats and dangerously accurate attempts to make fire.

The reflections of this book's title are of course the author's own and as with all autobiographies we are left wondering how honestly people and events have been portrayed. This hardly matters since, ultimately, the most haunting impression is the relationship between Galdikas and her subjects or, more generally, between humans and orangutans. Galdikas is a bridge between different worlds and through her eyes we experience an unsettling blurring of the distinction between human and animal. When a cook is raped and the rapist happens not to be a human and when Galdikas's adopted child is removed by her jealous husband when she is out of camp and that child also happens not to be human, the forests of Borneo begin to take on an other-worldly feeling. Yet while Galdikas may be a bridge, she really only serves to accentuate the distance between the two worlds of ape and human. This is no better exemplified than in a scene in which adolescent captive orangutans gaze off in a distant reverie while masturbating through the bars of their cage into the hands of their embarrassed owner, the genteel wife of an army commander.

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In contrast, Kanzi: The Ape at the Brink of the Human Mind comprises a determined effort on the part of its authors to dismantle the barrier between ourselves and another species of ape. Ensconced in the Language Research Center, Atlanta, Sue Savage-Rumbaugh is chiselling away at the cracks that she sees appearing in our concept of human uniqueness. Her subject is the bonobo, or pygmy chimpanzee, a maverick that has recently received much media attention not least as a result of its sexual proclivities.

The bad guys in this story are the linguists, inherently critical of ape language research since it undermines the primacy of language as a tool for laying bare the design of the human mind. This research faltered in the 1970s with the defection of Herbert Terrace who concluded that the thousands of hours teaching his subject, Nim Chimpsky, sign language had resulted in little more than conditioned associative learning. The Chomsky school, for whom grammar was the beginning and end of language, was vindicated, since grammar was exactly what eluded Nim. Savage-Rumbaugh still seems to have difficulty publishing her work and the unlikely choice of a popular science format (with popular science writer Roger Lewin) for this heady mix of linguistics and comparative psychology may reflect her frustration being unable to communicate the import of her work to scientists whom she feels will only see the design details, not the animal itself.

In her research program, Savage-Rumbaugh showed considerable foresight in choosing to concentrate on words rather than on grammar: in particular on words' vital properties of reference and intentionality. Since language is a communicative act, Savage-Rumbaugh embraces this fact, providing naturalistic scenarios for her (originally common chimpanzee) subjects to "talk" to each other in order to obtain goals. They achieve this through the use of a keyboard in which arbitrary symbols are used as words.

Kanzi, a bonobo, stands alone, however. First, he began to use his mother's keyboard spontaneously, without training, in the manner that human children begin to talk. Second, if we are to believe events in this book, Kanzi not only appreciated grammar but went so far as to invent grammatical conventions for his own use. Add to this his apparent ability to understand spoken English and a flair for fashioning flint tools, and the authors' case for a living, breathing model of hominid ancestors becomes ever more persuasive. Savage-Rumbaugh takes a far-reaching view of the implications of her research for human evolution. The idea that neurally, biologically, another animal may be capable of language implies for her that language is a recent, cultural invention like agriculture. This is an upsetting conclusion for guardians of human uniqueness, and in these speculative chapters Savage-Rumbaugh is sure to upset many people.

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Theoretical axe-grinding and the exacting nature of science can cause us to lose sight of the wonder of its creations. The truly chilling prospect that Kanzi raises does not concern human origins, but Kanzi himself. When the philosopher Thomas Nagel asked "what is it like to be a bat?" he concluded: we can never know. What is it like to be a bonobo? What might Nagel have penned after a discussion with Kanzi?

Thomas Sambrook is a member of the Scottish Primate Research Group, Universities of St Andrews and Stirling.

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