Rain lashes the canopy gathering in fat droplets that slither down through the murky stillness to the forest floor below. Here, a band of men is clambering over buttresses, ducking beneath vines twisted into braids as rigid as stone. At their head is an impish figure, his exuberant moustache and hat sagging in the sultry air. He takes a swig of brandy. He’s spent months in this boundless rainforest, sustained by little more than honey, the odd scrap of monkey meat, and longing. The object of his obsession? A creature known to local tribes as ‘njena’, a myth-like beast never before seen by Western eyes, a ghost of the Dark Continent.

The man stops, stoops and examines a root fragment. It has been torn from the ground and gnawed. Ahead, a small tree shakes in the windless forest and the crack of a branch ricochets through the understorey. Signalling to the others, he swings his rifle from his back and sets off into a tunnel torn through the foliage. Wrenching aside a curtain of leaves, he stumbles from the treeline and there, before him, stands his life’s goal – the ‘king of the African forest’.

‘It’s a sight I shall never forget,’ the man will later write. ‘It rose on its hind legs, a hellish expression of face like some nightmare vision, eyes flashing with fire. It gave vent to roar after roar like the roll of distant thunder, beat its breast in rage – and then advanced...’

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It’s just before noon in the pygmy village of Oleme. Huts of bamboo and compacted mud line the clearing, their overhanging roofs of neatly layered marantaceae leaves burnished silver by the sun. The village is deserted, save for the central, tin-roofed kandza. Inside, a brace of drums, made from duiker antelope skin stretched across hollowed-out logs, are being pounded, rhythmically accompanied by animated clapping and singing from the 90-strong population thronging the open-walled building. In the centre, a young man and woman dance frenziedly, their shell anklets clacking, grass waist-ties thrashing around them, their sweat mingling with bodypaint.

Set on the fringes of Odzala National Park in northern Republic of Congo, Oleme is some 200 miles east of where Victorian explorer – and incorrigible sensationalist – Paul Du Chaillu ‘discovered’ gorillas. In Congo Basin terms, it’s the narrowest of margins. This watershed of the totemic river is an 800,000-square-mile sprawl of nature at its most irrepressible, its footprint akin to that of a small continent. Out of this Equator-straddling expanse, Du Chaillu emerged in 1859, laden with 20 great ape skins and unverifiable tales of the ferocity and cunning of these ‘hideous half-man, half-beast’ creatures.

Charles Darwin’s seminal work On the Origin of Species had just been released, and suddenly there was meat to add to the bones of evolutionary theory. The French-American explorer found himself fêted wherever he went.

The singing and clapping continue, the intensity rising with the heat. The dancers’ faces betray the strain. It may not look it, but theirs is a great honour. ‘We dance to connect with the spirits of the forest and to show our appreciation,’ says village elder Ngouma Frederick, his diminutive frame consumed by a floral mustard robe. ‘We must please them or the forest will not provide.’

For these people, the boundary between the physical and spiritual worlds is porous. Ancestors live on around them, communicating through everything from birdsong to the intonation of a chimpanzee cry. It’s a bountiful forest – but clear lines exist. Gorillas are highly sought after on the black market for the perceived medico-magico properties of their limbs, yet to hunt them is to offend the spirits – not to mention the forest people’s innate sense of evolutionary affinity.

‘We have a bond with the great apes,’ says Ngouma, as the drumming finally abates and the people disperse. ‘You just have to look at the hands, the fingernails, the way they carry themselves – they are so human.’