On the one hand, we cannot assume that animal expressions have any relation to similar expressions in humans. See for example how the misunderstanding of facial

On the one hand, we cannot assume that animal expressions have any relation to similar expressions in humans. See for example how the misunderstanding of facial expressions between great apes and humans (in both directions) has often lead to violence, and they're our closest relatives. However, I have a pet* theory that the long evolutionary history of dogs with humans has little by little made their facial expressions converge towards reasonable approximations of human expressions. Which of the ancestors of modern dogs were more likely to survive in the company of humans: those whose expression looked human-happy when the dog was feeling a positive canine emotion? Or those whose expression looked human-happy when they were feeling aggressive, fearful, disappointed, etc? * No pun intended