i was wondering if goblins were somehow just created like humans and elves,
or if they were a cross-breed of some other creatures.
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According to Tolkein, before the movies, Orcs and Goblins were not different creatures.
Quote from Tolkein:
"Orc is not an English word. It occurs in one or two places [in The Hobbit] but is usually translated goblin (or hobgoblin for the larger kinds)." —J.R.R. Tolkien, Preface to The Hobbit
Quoted from this site: http://lotr.wikia.com/wiki/Goblin
History of orcs is the real thing you need to look at.