In posts where people look for a dog walker I often read things like "my dog is afraid of big dogs" or "my dog is afraid of (e.g.) German Shepherds". Does science support these claims? I.e., that dogs understand the size of other dogs and can distinguish between (human created) breeds?

My anecdotal experience regarding size, from having small dogs like Toy Poodle and Pomeranian to medium/large dogs like Golden Retriever, and a variety of dogs inbetween these sizes, is that e.g., the GR was afraid of/respected the Pomeranian despite the GR could kill the Pomeranian with one bite (a typical example would be if I gave them a marrowbone each, the Pomeranian would steel the GR's bone and the GR would just sit watching the Pomeranian having both bones, clearly unhappy with the situation but not doing anything about it).

My personal belief is that dogs, instinctively, can distinguish between sex, age (adult/puppy) and (some) health status when they meet other dogs, but NOT size and breed. If a dog reacts to size and breed it is because its owner reacts to certain sizes and breeds and the dog has learned from the owner, not because the dog itself understands the difference, but what does science say about this?

Edit: with size I refer to that humans usually don't pick a fist fight with someone twice their size, so to speak. If a human has a conflict with someone, they usually consider the other parties physical capabilities before starting a fight. Dogs, OTOH, frequently can be seen as being submissive to another dog that is much much smaller, which, from a human perspective, doesn't make any sense, from a pure physical perspective.

1 Answer 1


Dogs have no concept of breed. Seeing a Poodle or German Shepherd is for them like seeing a brunet or a bald person is for us. They just look different.

Size is not automatically understood as a measure of power or respect, either. Properly socialized dogs who learned natural dog body language as puppies usually negotiate their rank and respect towards each other within the first minute of meeting.

However, dogs who were not properly socialized and didn't have many opportunities to practice dog communication struggle with this process. Due to Covid lockdowns we are faced with an entire generation of poorly socialized dogs right now. And if they have a tendency to be aggressive or dominant, a bigger size helps them bullying other dogs, for example by towering over them or physically pushing them to the ground.

On the other hand, if a dog (of any size) had made bad experiences with a certain dog of a certain breed, they might connect the look (size and breed) of any dog they meet with that bad experience and be afraid of all German Shepherds.

And lastly, as you correctly mentioned in your question, dogs do react to their human's behavior. If an elderly lady with a small dog is afraid that any bigger dog may attack "her baby" and acts fearful whenever she sees a big dog at a distance, her own dog learns from her nonverbal clues that it should be afraid of big dogs.

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    ...or the small dog tries to protect it's old lady. Commented Dec 10, 2023 at 13:19
  • We suspect our dog, Mickey, had an incident or two at dog daycare because he has a stereotype against a couple specific breeds. Regardless of how sweet they are his ruff will go up. Commented Dec 15, 2023 at 20:32
  • @ChristopherKlaus Have you verified that with a double blind test?
    – d-b
    Commented Dec 17, 2023 at 12:50
  • @d-b It happens regardless if me or my wife are walking him. That said, no double blind test. ;) Commented Dec 18, 2023 at 5:15

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