Orcs evolved from the Neatheans that moved into the vast, monster filled jungles of the southern continents. They had to adapt to become the prime predators, so they evolved a nocturnal sleep cycle, darkvision, elf-like super hearing, green skin and fur to act as camouflage, and enormous canine teeth and claws to serve as vicious weapons.
Larger and larger packs of Orcs unified over time, helping them develop religion and culture. Present day Orcs keep a proud, strongly spiritual warrior culture; And though they have never been active aggressors toward the other humanoids, they are still widely misunderstood and mistrusted. The hatred they garner from Humans goes back centuries, back to the many bloody border wars that now lay in stalemate.
The eyes of an orc have evolved to maximize visibility in near or completely dark environments. The pupil of their eye has developed into horizontal slits, much like the eyes of a cat. This pupils can dilate the extent of their entire eye allowing them to see things others would miss, however when their pupils are fully dilated they loose much of their depth perception. The remainder of their eye is almost completely made up of almost entirely by their iris, allowing more room for the pupil to dilate. This allows orcs to make use of even the smallest amount of light available.
Orcs have the largest eyes of any of the humanoid races in comparison to the size of their face. Due to the evolution of their eyes for nocturnal use they have lost much in the way of color definition. They can see blues, greens and some shades or red and yellow, but almost everything else are differing shades of gray.
Orcs ears evolved into large, pointed bat-like ears. Although the outer structure of the ears seems to be cosmetic evolution, the structure of the outer ears exists to only further the inner workings. Their sense of hearing far exceeds that of humans. It might well be on par with elves, however orcs ears have also evolved to allow for echolocation. A tool they use often when traveling in hunting parties.