Goblins are often viewed as evil little creatures, but that image simply sprouts from circumstance; goblins aren't inherently evil, but their nature makes it easy for them to be controlled by an evil force. A more apt observation would be that goblins are extremely adaptive creatures, to the point of being able to alter their physiology over time to adapt to circumstance. Their protean nature is basically humanity on steroids, albeit a bit less intelligent on average.
Goblins have been shown to be capable of adapting to city life, standing taller, cleaning up their speech, and even modifying their bone structures to fit into human clothes. Surrounded by academia, some experiments have found goblins becoming capable of writing, philosophy, and somewhat worryingly, very capable with magical research.
Goblins tend to reflect their environments; goblins raised in dark caves attain superior darkvision and often have giant eyes; desert goblins, on the other hand, have thin eyes, low figures, and tougher skin. Frost goblins have thick skin and better ability to build fat deposits, and so on.
They mirror aspects such as alignment and personality as well, and as they are often born into evil environments, turn out evil. However, this fate can be reversed if they are forced into a different kind of society, though the adjustment may be a bit rocky, and somewhat bloody. The longer a goblin is in one environment, however, the less able they become to adapt to a new one.