* Evolutionary History: Dew claws are actually remnants of the fifth toe that most mammals have. Over time, as dogs evolved to be efficient runners, the fifth toe became less useful for running and gradually reduced in size. However, the gene for the fifth toe hasn't completely disappeared in all breeds.
* Breed Differences: Some dog breeds still retain the dew claw on both the front and back legs, while others have lost them completely or only keep them on the front legs. This is due to selective breeding practices. Breeds like Bernese Mountain Dogs and Great Pyrenees typically have dew claws on both front and back legs.
* Function (or Lack Thereof): While dew claws may have helped with climbing or grasping in their evolutionary ancestors, they don't serve a significant function in modern dogs. In fact, they can be prone to injury, especially on the back legs.
Important Note: If a dog has dew claws on their back legs, it's usually a good idea to have them removed by a veterinarian when they are a puppy. This prevents potential injuries, especially if the dog is active or participates in dog sports.