How bad it gets, you can't imagine
The burning wax, the breath of reptiles
God is not mocked, he knows our business
Karma could take us at any moment
Cover him up... I think we're finished
You know it's never been so exotic
But I don't know, my dreams are vicious
We could still end up with the great big fishes 

The Tcho Tcho owe their peculiar characteristics to their origins. They are direct descendants of the stock of proto-humanity taken by the Elder Things from Africa and bred by them as servants, and as potential replacements for the rebellious shoggoths. The germ plasm of the pre-Tcho Tcho was altered in a manner similar to that of the shoggoths, both to increase their intelligence and to increase their biological flexibility and receptiveness to further modifications. It is this trait that accounts for the automutagenic effects of Tcho Tcho diets.

During the upheavals caused by the shoggoth revolts and the decline of the elder things' civilisation, some of the proto-Tcho Tcho escaped Antarctica through portals to the dreamlands (always a menace in antarctica due to the time/space/logic warping effects of Kadath and the God Trap). They passed through to the cognate location of the Plateau of Leng, where exposure to the hyperdimensional energies of the place and crossbreeding with the Mani Nigri caused their Elder Thing-altered genome to assume its diet-assimilating structure. Some then made their way to the other real-world cognate area of Tibet, where they mingled with the Tibeto-Burman language speaking groups and spread across South-East Asia. Though they rapidly became feared and reviled by the humans surrounding them, their ability to assimilate genetic structures from other groups means that within a generation, any group of Tcho-Tcho will have many members who look identical to, and have probably infiltrated, the surrounding groups, making them very difficult to exterminate. As well as appearance, Tcho Tcho assimilate the genetic "strong points" of their victims - thus Tcho Tcho are immune to a wide variety of diseases and poisons, and may well be stronger, faster, and more attractive than average.

Some Tcho Tcho are able to employ mythos energies to go beyond genetic assimilation and assimilate knowledge from the structure of their victims' brains. Powerful Tcho Tcho may also be able to assimilate genetic characteristics from wildly different (insects, plants) or even non-terrestrial (eg Mi Go) biologies. Tcho Tcho without command of the powers of the Mythos are more likely to face an agonising, cancerous death if they attempt such a feat as their body tries to incorporate radically different DNA. However, once a Tcho Tcho sorcerer has successfully incorporated such characteristics he may pass them to his descendants - thus there are several reports of Tcho Tcho with insectile (Tcho Tcho Queens) or reptile based biological and social systems.

A common punishment for criminal or deviant behaviour among Tcho Tcho groups is to force the miscreant to live on the meat of some useful lower animal (eg a dog). The resultant pathetic half-human, half-dog can then be used as a guard, warrior, or back-up lunch.

It would be possible for a Tcho Tcho to safely live on a diet not containing human meat, but only if it contained very little DNA in an intact state - in other words, boiled to a soggy paste to thoroughly denature the proteins. Since Tcho Tcho rarely have degrees in molecular biology or the opportunity to leave their cannibalistic societies, this solution is unlikely to be arrived at by many. Tcho Tcho living "in the wild" prefer a diet of human, then other primates, then mammalian predators with characteristics admired by the Tcho Tcho (e.g. tigers) then vegetables which experience has shown are unlikely to be inadvertently assimilated. Herbivore and non- mammalian meat is only eaten by the lowest members of the tribe.

Tribes which have assimilated non-mammalian characteristics, eg hive-queen Tcho Tcho, will eat large quantities of the relevant animal (eg ants, bees, wasps) to reinforce their genetic matrix.

Tcho Tcho sorcerers fearing death by old age have been known to take up vegetarian diets and self-mutate into tree-like beings, spending the rest of their virtually immortal lives anchored to the earth in a dream-like state. They may be contacted through spiritual or dreamlands procedures, or woken by means of magic, if their tribe needs advice or faces a crisis.