We are two social species that have developed a bond 15,000 years old. Man and dog share so much and apparently we share stress too. A new study out of the UK shows if you're stressed, your dog is stressed. The researchers measured cortisol levels in human hair and dog fur. Cortisol is a chemical released into the blood during stress. The study found that the cortisol levels in humans and their dogs often sync up. Click the link for more of our discussion on dogs and how they read our emotions.