Robinson, Phil (1882) Under the Sun, Roberts Brothers, p. 120

For the establishment of the soko’s individuality, however, there are teeth, skin, and skulls in existence, and the last have been declared by Professor Huxley to be human. They were brought from Africa as the fragments of a great ape which certain natives had lately eaten, and which they themselves called "meat of the forest."
Nevertheless, the Professor declares that they are the vestiges of defunct humanity, male and female. After, such a verdict the soko at once takes rank as one of the most interesting mysteries of nature. Is it human or not? ls it the chief of monkeys or the lowest of men? Dr Livingstone was not quite certain, and Mr H. M. Stanley was only half-convinced.
In reviewing the work of the latter explorer for a London journal I drew special attention to the soko, for though actually known only by report, the repeated references to it make this ape-man one of the features of the book. It is true that on one occasion Mr Stanley actually startled to its feet a great monkey person that was asleep on the river-bank but his boat was shooting down the stream so swiftly that he could not tell whether it was beast or man. Circumstantial evidence of the existence of a half-human creature, however, thrust itself upon the explorer day after day.
When editing Mr. Stanley's "Through the Dark Continent," I heard from the explorer and read in his notes much that was not published. His Soko lore was considerable; but in a few words his man-ape problem is this. The natives gave Stanley skulls, teeth, and skins of a creature they called an ape. Professor Huxley says the skulls are human. The teeth and skin are not.
In Manyema, in the Uregga Forests, at Wane Kirumbu, at Mwana Niabn, the soko was heard after nightfall or during broad daylight roaring and chattering. At more than one place its nest was seen in the fork of a toll bombax, and both at Kampunzu and a village on the Ariwimi its teeth, skin, and skulls were obtained from the people, who never differed in their description of the creature they called "the soko," and insisted that it was only a monkey. The skulls at any rate have been proved to be human, and the teeth are some of them human too but if the tough skin thickly set with close grey hair came off the body of a man or a woman, he or she must have been of a species hitherto unknown to science.
For as yet no family of our race has confessed to a soft grey fur, nearly an inch long in parts, and inclining to white at the tips but such is the skin of the soko, the creature whose skull Professor Huxley says is human.
Two fascinating theories at once suggest themselves to help us out of the soko mystery, for, promising that Mr Stanley and Professor Huxley are both, of course, noting in good faith, it may happen that under either theory the thing described by the tribes along the Livingstone [Congo] river as "a fruit-stealing ape, nearly five feet in height, and walking erect with a staff in its left hand," may prove to be human. The first is that, the tribes who eat the soko are really cannibals, and that they know it, but feeling the shame on this point which is common to nearly all cannibals, they will not confess to the horrid practice, and prefer, when on their company manners with uneatable strangers, to pass off their human victims as apes.
The other is that there really does not exist in the centre of the dark continent a race of forest men so degraded and brute-like that oven the cannibals living on the outskirts of their jungles really think them to be something less than human, and as such hunt them and eat them.
Either theory suffices to supply the "missing link," for if if it be that the skulls of the soko are human skulls, then the tribes of the Livingstone have among them a furry-skinned race of men that feed by night and have no articulate speech.
If, on the other hand, these furred creatures are so like monkeys that even savages cannot recognise their humanity, and yet so like men that even professors cannot recognise any trace of monkey in their skulls if the person called the soko must be a very satisfactory “missing link” indeed, for it is essential in such a person that he should so nearly resemble both his next of kin as to be assignable to neither.