I think emotions are innate, but the learning does play an important role in the activation of emotions. The example with monkey and snake fits very well with this question. By observing the mother's reaction to the snake, the little monkey learns to associate fear (the ability built-in by evolution) with the snake (stimuli). In simple words, little monkey doesn't learn to fear, it learns to fear the snake. This association is created unconsciously in the brain and the next time little monkey encounters a snake emotion of fear occurs automatically.