Orcs have a very distinct appearance, one that is bestial and frightful, inhuman to be sure yet still bipedal, creatures of nightmare that seem to typify our greatest fears. What kind of biology and details of anatomy might best exemplify these exercises? Are there any models in our real world that could give us information that would help us design and create more accurate goblins and orcs?
While bipedal, orcs are clearly not human. They appear to be more related to our simian cousins, with greater strength, different morphologies and such. Which great ape would an orc most likely resembble? Perhaps they are a mixture of the human and the gorilla, with greater jaws, massive shoulders and backs, smaller legs and deep chests. I like the idea that as an orc grows in power his skin changes color, much as the alpha gorilla would turn silver. Perhaps orcs are light green at birth, and their color ever darkens until they pitch black upon their ultimate supremacy and size.
It would make sense then that goblins are born more like gibbons, and as they grow more powerful they increase in size and strength so that they appear to be more like chimpanzees, small, wiry, disproportionately powerful. They would have less jaw strength, greater motion and flexibility, greater speed even, trading the power and strength of an orc for the nimble agility of a chimpanzee.
This would also accord well with their new life spans, which is postulated to explain their violence and lack of culture. Gorillas live from thirty five years to fifty, depending on whether they're in captivity or not, which means that it accords well with orcs as well.
So an orc could be born little larger than a chimpanzee, light green, feckless and weak, and only with experience, with age, with the accumulation of power would they grow in size, until they became chieftains or leaders who would be the size of fully grown gorillas, weighing hundreds of pounds and with dark, charcoal skin, matt black and stretched over their great musculature. Possible!