According to new research, since all species share a common ancestor if you go back far enough, Darwin reasoned that humans would use the same muscles as other animals to express emotions. And although a dog is different from a mouse, all pets probably express emotions in much the same way that humans do, according to Jeffrey Mogil, a psychologist and neuroscientist at McGill University in Montreal, senior author of a study published online in the journal Nature Methods. Continue reading for more.