If certain inputs into a function yield nonsense results, clearly the function is poorly defined. :/
Some of you want to include human as a maximum, so alter the function to take this as such. The hybridization function is a step in the right direction.
We need several functions to create various blend-forms/ hybrids.
(I tried to write a function that follows an asymptotic curve here, but ended up confused with a non-species.)
We need: animal anthropomorph/civilization function, hybrid function, man animalistication/feralization function.
Giving man animalistic features seems to me a more reliable method of creating animalmen than the reverse, mainly due to the hands thing. a 10%anthropomorphised fish is no fishman in my book but rather a facefish or walkingfish. In order to earn the title animal-man, the creature needs to be more man than an ape. And apes are 99% like human already!
Also fantasy hybridisation works by magic and not 100% realworld genetics, so we need to add a bit of that too. Randomised creature gen we have, combining various Body parts from various creatures (and other stuff).
Centaurisation function, faunisation function, mermanisation function, demonification functions, etc., generally are similar grafting functions, but more specific. eg Take humanoid, replace legs with a quadruped, equine creature or fish tail, or snaketail. Faun and demon are more anthropomorphic though, but with altered legs, added horns, tusks, wings, fur, scales, etc
Possibly the method could
evaluate the bodytemplate of the target creature and take (predefined ?) characteristics from it, such as skintype, horns, tails, etc and just add/replace those to the basic human bodyplan. Add some randomized wholly transplanted bodyparts, head, or just the eyes, ears, teeth, nails/claws.
Tags such as [breathwater] [intelligent] [grasping] and whatnot are linked to bodyparts? (gills, brain, hands/teeth)
Taking up the f(elf,-0.5)=orc ,f(hobbit,-0.5)=gollum, etc argument:
this is more an allignment function, though the evil one did only ever detract from the originals.
This argument allows for: f(human, human)=highmen of Beleriand, who were stronger of will and body and lived much longer than the men in the time of the Fellowship.
[/rant]