Here's why:
* Pavlov's research focused on general principles of learning: He was not specifically interested in breed differences, but rather in the universal processes of classical conditioning.
* Availability and cost: In the late 19th and early 20th century, purebred dogs were less common and more expensive than mixed breeds. It's likely Pavlov used readily available dogs from shelters or local populations.
* Pavlov's descriptions: In his writings, Pavlov never mentions specific breeds, focusing instead on their behaviors and responses.
So, while we don't know the exact breed, it's safe to say that Pavlov's dogs were likely a mix of different breeds. They became famous for their contributions to our understanding of learning, regardless of their breed.