Charles Darwin was the first author to compare human and animal emotions. At that time, animals were largely perceived as automatons, merely supplying robotic responses to environmental stimuli. That notion has been perpetuated in one form or another all the up to the time of famous behaviorist B.F. Skinner.
Fortunately for dog lovers everywhere, there has been a slow but steady movement in the animal behavior sciences to design more rigorous, less biased experiments to detect and measure animal emotions. Today, most researchers agree that domestic dogs are roughly equivalent in emotional development to a human toddler (age 2-2 ½ years old). Dogs (and cats) exhibit all six of the “primary” emotions – happiness, sadness, fear, anger, disgust, and surprise (yes, many psychologists consider surprise to be an emotion, even though it wasn’t depicted with the “big five” in the recent blockbuster animation Inside Out).
Researchers haven’t confirmed that dogs experience more complex emotions. For example, many owners think that dogs show guilt or shame when they are caught being naughty (such as rummaging through the trash bin). In one illustrative study, innocent dogs displayed the same “guilty” behavior as did guilty ones, even when the human was the one to upend the bin and throw trash all over the floor! The behaviors displayed by “guilty” dogs are triggered by either an environmental cue (like garbage strewn across the floor from an overturned bin) or by the body language or tone of the human walking in on the transgression.
Some researchers argue strongly for the presence of more complex emotions in dogs, but to date, the data simply doesn’t support their claims. Then again, twenty years ago, a scientist could lose their status and funding if they claimed that animals had any emotions at all. With new research into neurobiology and anthrozoology, perhaps someday we will be able to identify all of our pets’ emotions.