Is fear innate or learned by dogs?

Dogs are physically unable to formulate negative emotions because the complexity of their brains are not as developed as ours. Dogs do not become fearful of something, they are naturally born with certain instincts that guide them through life, such as their instinct of fear.

^ NOT TRUE.

My dog has plastybolsaphobia (fear of plastic bags) and it was NOT just natural cause i shook a bag to put something in it and her ears went back and she started shaking but she was fine all the times before when i had plastic bags.