There is a king, a prime minister and a first lady," my Tanzanian guide Kabeth H Kabeth says, describing the hierarchy of M-group, an extended chimpanzee family used to encounters with researchers and tourists in the Mahale Mountains National Park, on the forested shores of Lake Tanganyika. We look on as the wild chimps appear to act out a complex and violent classical drama: a 21-year old chimp named Pim, who took over as alpha male, is inexperienced, restless, and perhaps a little mad; scientists have observed him abusing his mother, behaviour as deviant for chimps as for humans. Kalunde, a 47-year-old former alpha, is physically shrunken and forced to exert influence through others. He tried to keep Alofu, the previous dominant male, in power by inviting an exiled ally, Fanana, to rejoin the community.
Pim took advantage of the failed coalition but may not last long because M-Group females, free to join another group, fear and loathe their chimp Oedipus Rex.
The 1,613 square-kilometre Mahale Mountains National Park is larger but less famous than Tanzania's Gombe Stream National Park, where a young Jane Goodall discovered that chimpanzees make and use tools to fish for termites. Rising 2,438m above Africa's deepest lake, the Mahale range of parallel green ridges, fingered by mists, falls to a shoreline of boulders, rock coves and crescents of white sand. The water reflects green trees, blue sky and rolling clouds, a palette of teal, indigo and gun metal grey, transparent and thickly textured all at once. In 1871 it took Henry Morton Stanley 236 days to march 1,930km inland from Zanzibar to Tanganyika's shore, where he found Dr David Livingstone, missing and presumed dead, resting under a mango tree. I've arrived on a five-hour flight in a Cessna from the safari gateway town of Arusha. A dhow, a vestige of the 19th-century Arab slave trade Livingstone sought to eradicate, has collected me from a dirt airstrip for the 90-minute voyage to my base for the next three days; Greystoke Mahale, a lodge on a beach inside the park not far from one of Stanley and Livingstone's old campsites.
In 1965, University of Kyoto primatologists established a Mahale Mountains research station and discovered that in addition to using tools, our closest relatives also know how to self-medicate with plants, including some that act as antibiotics. To preserve chimp habitat, the Tanzanian government gazetted Mahale Mountain National Park in 1985. Though it is one of the most beautiful spots in Africa, the park receives remarkably few visitors because of primitive infrastructure and the huge expense of long-distance light plane charters whose easiest alternative is a three-day train ride from Dar es Salaam to the port of Kigoma where a First World War-era ferry, the MS Liemba, may or may not leave on time, to connect 10 hours later with an appointment with park officials. Greystoke Mahale was founded two decades ago by an Irish bush pilot and former Sotheby's auctioneer, Roland Purcell, who pioneered African chimp-watching safaris. Named after the character in Edgar Rice Burrough's Tarzan story, Greystoke Mahale is accessible only by boat and has evolved from the original Arabian sultan-style tents to seven thatched A-frame suites inspired by Central African bandas better able to withstand sudden lake squalls. Facing the beach from the tree line, mine has a king sized wood-framed bed draped with mosquito netting and an upstairs platform reached by a ladder fashioned from a wooden dugout canoe. Much of the lodge structure is made of recycled dhows which bear slogans and proverbs according to Tanzanian tradition; my favourite, painted on a prow incorporated into the resort's sundowner bar reads, "Myenyefina hakosi sababu," or "Jealousy has no reason" - a pun and perfect short summation of Othello. Over a candlelit dinner of grilled pork, gingered carrots and coconut rice, Kabeth, the head guide, briefs the other guests and me on the rules of chimpanzee observation. Of the 700 or so chimpanzees living within the 1,614 square-kilometre park, the 59-strong M-Group, named after Mimikire, the original alpha male, have been observed for more than 40 years by scientists and are habituated to visits from dilettantes like us. Continual contact with humans has carried a price. M-Group's population has fallen from more than 100 in the mid-1990s and in 2006, 12 chimps died of a flu-like ailment in all likelihood caught from humans. To reduce the risk of contagion, park officials now limit chimp-watching groups to six guests who must wear surgical masks and stay at least 10m from the animals. Trackers will go out before we wake in the morning, looking for nests, droppings and fruit scraps and radio back as soon as they locate members of the group. Depending on the availability of fruit and where they have been feeding, reaching the chimps may involve a five-minute boat ride down the beach or a four-hour hike towards a mountain summit.
As we eat breakfast the next morning, the trackers signal that they have located Pim and some of his cohorts at a place that is a 30-minute walk behind the camp. "Be ready to go in 10 minutes," Kabeth urges. "If Pim decides to move, the others will follow. Chimps move so fast that they might be three hours away if we delay." We enter the forest behind the lodge carrying cameras, water bottles, rain ponchos and our small surgical masks, clambering up leaf litter paths, over fallen branches and under huge creepers. Where I see a wall of green, Kabeth sees a salad bar and pharmacy. There are primitive-looking, three-leafed cabbages, fragrant ginger, and wild liquorice, and plants that can cause abortions and ease difficult births and relieve diarrhoea, tuberculosis, and malaria. He shows us sticky furred pentalia leaves that chimps roll into cigars and swallow whole to rid their systems of parasites and tiny blue crotonia flowers that his Batongwe people, who once shared this same forest, squeezed for eye drops. Kabeth was born in the forest, from which the Batongwe were evicted when the park was proclaimed, and he points out surviving stands of mango, lemon, guava and raffia palm orchards, moss covered clay pots, and other village remnants.
M-Group members are sometimes separated by long distances. They recognise each other's voices; obsessive pant hooting and pant grunting (the former by subordinates to more dominant animals) is the chimpanzee equivalent of Twittering, indicating to both chimps and researchers who is hanging out with who, and who's up and who's down on the social ladder. We hear pant hoots before we see three barrel-chested male chimps knuckle running down the path; they are all bigger than any zoo chimp I have ever seen. Psycho Pim is trailed by Primus, the number three, and another young male, Orion, recognisable by a white scar on his glossy black back. When we catch up, Primus is literally currying favour, grooming Pim under saba florida vines. Then Pim screams and comes charging towards us down the path. Kabeth grabs us all in a protective bear hug and we stand up in a vertical cluster as Pim brushes past us on two legs, arms raised over his head. Mahale chimps sometimes shove humans off trails but have never harmed an observer. By contrast, one of Jane Goodall's famous subjects, a Gombe Park male named Frodo, once nearly broke her neck and, in 2002, killed and partially ate the 14 month-old daughter of a park employee. At only 52 square kilometres, Gombe Stream National Park is much smaller than Mahale, and some scientists say that when villages encroach on chimp territory it becomes natural for chimps, which hunt monkeys, to view small children piggybacking on their mothers' backs as food. Kabeth thinks Pim was reacting to an unseen chimp's pant hoot, not our presence. We are unscathed, although in the excitement I've stood on a nest of siafu ants, I now have ants in my pants and some are biting me. Old Kalunde has gone up a tall ficus tree. Commotion over, he descends to greet Michio, a long-faced 12-year-old male, and Matsue, his cute five-year-old sister. Eventually they all relax and Kalunde grooms his best friend, Mkombo, an infertile female. In addition to chimp-watching, Greystoke Mahale Lodge offers kayaking, bird-watching, snorkelling, and dhow sailing out on the lake, which is nearly 1.6km deep, holds 18 per cent of the planet's fresh water, and remains one of the purist bodies of water left on earth. Over its surface the hot humidity of the Congo Basin meets the cool air of the East African highlands and water temperature hovers at a tropical 80 degrees. That afternoon, with the lake mirror calm, we vote to take the dhow out fishing. The lake is home to giant Nile perch and kuhaye, a large edible member of the cichlid family. Within minutes of leaving shore, we all have hits, reeling in two pound kuhaye with turquoise-spotted cheeks, yellow backs and black-spotted silver bellies. Kabeth has brought along soy sauce and a tube of wasabi mustard and serves up sliced Kuyaye sashimi with wild ginger collected from the forest. It would be pure paradise, except for biting tsetse flies. A few hundred metres past the mouth of the Lubulungu River and its estuary clogged with canopic plants, a lone hippo pokes his nostrils, eyes and ears above the water. The dhow circles to scare off hippos, crocodiles and fish-eating water cobras, and we put on masks water cobras. We put on masks and jump in, hovering in shallow water over a rocky cove where there are a multitude of tiny cichlid fish that evolved from the salt water species which became landlocked when Lake Tanganyika formed over 20 million years ago. In the cove's natural aquarium I see fish with black and white checks, dangling whiskers, iridescent blue and green spots, and yellow stripes; fish shaped like torpedoes, inverted triangles, and even circles. There are mouth breeders - fish that carry fertilised eggs and hatchlings in their mouths - and cuckoo catfish, who manage to spit their own eggs into the mouths of mouth breeders, whose brood becomes food for the invaders' spawn. At the end of the afternoon, we catch sight of two black forms coming down to drink, wild chimps far from the habituated M-Group's territory. In Batongwe mythology, Kabeth tells us, chimps are ancestors who abandoned the life of villages, choosing to wander the forest and its waterfalls and shafts of sunlight filtering through the green canopy of trees. In this narrative of a reverse Eden, chimps refuse to speak with humans lest they be put to work. The chimps take one look at us and, perhaps disapproving, quickly move back into the trees.