Faces of wolf, dog and human (IMAGE) Experimental Biology Caption Faces of a wild gray wolf, a Golden Retriever domesticated dog, and a human, along with tissue samples from the orbicularis oris muscle for each species. In the photos the dog and human are actively using the zygomaticus and orbicularis muscles (note the dog’s upturned lip, which mimics smiling). The stained muscle samples reveal similarities in muscle content between dogs and people that likely contribute to their facial flexibility compared to wolves. Credit Anne Burrows, Duquesne University, top images copyright iStock. Usage Restrictions Credit must be given to the creator. Only noncommercial uses of the work are permitted. No derivatives or adaptations of the work are permitted. License CC BY-NC-ND Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.