A new study out of Michigan State University found that dogs' personalities CHANGE over time.
And in a lot of cases, they actually take on some of the big personality traits from their owners.
The researchers found that people who are outgoing had dogs that were more active and excitable . . . people who are unhappy had dogs that were more fearful and harder to train . . . and agreeable people had dogs that were less aggressive.
The results were a surprise to the researchers, who say, quote, "We expected the dogs' personalities to be fairly stable because they don't have wild lifestyle changes [like] humans do, but they actually change a lot."