Specific breeds definitely have tendencies towards behavioural issues. Breeds used for guard dog duties such as German Shepherds and Belgian Malinois are naturally alert and suspicious, which can make them more prone to anxiety and fear based aggression. Protection dogs such as Rottweilers and Mastiffs are often likely to show dominance aggression traits. And the smaller dogs such as Shih Tzu, Poodles and Pekingese often have a very close bond with their owner which makes them more prone to separation anxiety. I would always recommend someone researches a breed closely before they decide to bring a new dog into their family so they can be aware of any potential behavioural issues, and make sure the dog is right for their situation. But the real influence comes from the owner – I don’t believe any dog breed is always aggressive or always fearful, a great deal of the behaviour comes from how we as people train and treat our dogs.