The people who became yuan-ti were one of the original human civilizations. Their society built great temples of stone and forged metal into armor, tools, and weapons. In their ceremonies they paid homage to the snakes as the embodiment of the qualities they most appreciated. They developed a philosophy of following intellectual pursuit, allowing them to focus their energy on personal advancement and expanding their energy on personal advancement and expanding their territory. They believed themselves to be the most enlightened mortals in the world, and in their hubris they sought to become ever greater.
The serpent gods of the primordial world heeded the prayers of these people and hissed demands into their ears. The people were granted reptilian forms from their devotion to these gods to be molded in their likeness. Freed from the limitations of their human bodies, the yuan-ti used their new abilities to conquer new lands and expand their borders.
One Race, Many Forms
The bodies of all yuan-ti have a mix of humanlike and snakelike parts, but the proportion varies from individual to individual. After the initial metamorphosis of the humans, their society quickly coalesced into a caste system based on how complete a person's transformation was. The vast majority of yuan-ti fall into three categories-abominations, malisons, and purebloods-while the mutated broodguards and exceedingly rare anathemas have their place in the hierarchy as well.
All yuan-ti can interbreed. Females usually lay clutches of eggs, which are stored in a common hatchery, although live births aren't uncommon. A mating between yuan-ti of different types almost always produces eggs that hatch into yuan-ti of the weaker parent, so most choose partners of the same type in the interest of maintaining the strength of their personal bloodline.
The yuan-ti have abandoned their humanity and many consider non-serpentine humanoids to be lesser creatures, barely more civilized than common apes. Although some purebloods are able to reproduce with humans, most are disgusted by the idea and would do only if seduction is necessary for a pureblood to preserve a role as a confident or advisor in human society. The very rare offspring of such a union are always purebloods, although they may appear fully human at birth and for several years afterward.
The yuan-ti know rituals that can transform an individual into a more powerful type. The cost and time required to perform the ritual is prohibitive, and as a result most yuan-ti never get the opportunity to undergo such a transformation. Every use of the ritual must be modified to suit the individual undergoing transformation, and requires rare herbs, exotic magical substances, snakes, and depending on the yuan-ti society, one or more humans to be sacrificed and eaten as part of the procedure.