Hominids of the Ringworld
The Hominids of the Ringworld, like the humans of Larry Niven's other works about the Known Space fictional universe, are descendants of the species called the Pak, whose "breeder" stage resembled Homo habilis, and who utilize a symbiotic virus (which grows inside a plant called Tree-of-Life) to then develop into a hyper-intelligent Protector stage. The Pak Protectors built the Ringworld, but for some unknown reason, the Protectors and the Tree-of-Life died off, leaving the Breeders to breed and mutate randomly. The ecology of the Ringworld was left with many empty niches, and as the breeders evolved they moved into these niches, developing into a bewildering variety of species—predators, herbivores, aquatic mammals, tree-dwellers, etc.
By the time of the setting of the novel Ringworld, there were hominids occupying every possible environment on the Ringworld except the bottom of the two deep oceans. Examples include the high altitude adapted Spill Mountain People (actually many unrelated but similar species created by parallel evolution; the Spill Mountains are far apart, and the Spill Mountain People cannot travel the lowlands, so each group evolved in isolation), the carrion-eating Ghouls who serve as both cleanup crew and undertakers to the other species, and the Grass Eaters, who graze on plants and travel in herds. Arguably the most significant species are the City Builders, who spread across the entire Ringworld and mastered interstellar travel using Bussard ramjet motors cannibalized from the Ringworld's orbit-stabilizing system. Eleven hundred years before the events of Ringworld, they experienced a technological collapse (later found to have been engineered by the Pierson's Puppeteers), known as the Fall of the Cities. This phrase is not a metaphor; the City Builders had mastered magnetic levitation and had many floating buildings thus supported. Even a millennium after the Fall, the City Builder language is still used as a lingua franca on many parts of the Ringworld. Many also practice rishathra (inter-species sex for diplomatic purposes), a practice apparently started, or at least formalized, by the City Builders.
Notable hominids include:
The Red Herders: A monogamous species, short in stature, who herd animals and are carnivorous. Each group of Red Herder raises a single species, and when groups meet, they exchange different types of meat. They do not engage in rishathra.
Vampires: Actually hundreds of species, they all have in common their diet and means of attack. They are barely sentient, possess little intelligence, and like their namesakes on earth, they survive by draining blood from their victims. Vampires exude a scent which other hominids find arousing to the point of losing their senses. Other hominids will strip naked in an attempt to make rishathra with vampires, at which point the vampires will bite them.
The Machine People: They resemble humans in most regards, but have a different hair pattern. They are mostly bald, but have a ridge of hair along the base of their skull, and usually a fringe of beard, even on females. They are the most technologically advanced hominids on the Ringworld after the City Builders, and base their economy on trade and vehicles fueled by ethyl alcohol. They have also mastered gunpowder. Other hominids are often suspicious of them, as many who produce their fuel learn to drink it, with deleterious results to their societies.
Grass Giants: An herbivorous species, but very warlike. They stand one to three feet taller than other hominids, and wear heavy armor. They are led by a single chief, called the Thurl, who has sole mating rights with females. The Thurl often leaves the main group, at which time the other males mate, under the adage, "What the Thurl doesn't see, didn't happen." They mainly warred to protect their grazing grounds, and often came into conflict with the Red Herders. Louis Wu negotiated a treaty between the two, and since then, they have lived in peace.
Gleaners: The gleaners follow closely behind the Grass Giants after they have grazed. They feed on the insects exposed by the Grass Giants. They are diminutive and diurnal, unable to remain awake during the night hours.
Hanging people: Various species of arboreal hominids
Ghouls: The ghouls are among the most widespread of hominids. They are carrion eaters and carry out all the funeral rites of all the hominids of the Ringworld. They are nocturnal, but can function during daylight hours if necessary. They play musical instruments and take their names in the common tongue of the Ringworld from those instruments. Many consider them masters of the Arch (the natives' name for the Ringworld), due to their ability to communicate seemingly instantaneously with each other across tremendous distances. In actuality, they communicate using a code with mirrors along the rim wall, in cooperation with the Spill Mountain People.
The Spill Mountain People: A series of tubes draws sea bottom muck, called flup, from the Great Oceans and pumps it to pipes at the top of the rim wall. The flup drops down and the accumulating pressure compresses the flup into rock which forms the Spill Mountains. Along the tops of the Spill Mountains, similar hominid species live, but all are called the Spill Mountain People. They work to maintain the communications between the Ghouls, and are adapted to high altitude life, with its low oxygen level and cold temperatures. They are the one species that regularly interacts with Protectors, and occasionally, a Protector will take one of them to be transformed into a fellow Protector.
River People: A hominid species adapted to an aquatic lifestyle. They have very flat noses and almost no chins. River people are covered in fine oily hair and their females have exceedingly flat breasts.
Weavers: A people aptly known for their weaving abilities. Their creations are treasured for thousands of miles around their home. They were a favored species of Louis Wu, and are the recipients of one of the Hindmost's stepping disks.
Sand People: A hominid species that lives in the deserts at the base of the Spill Mountains.