Even animals that don't have spindle cells, such as dogs, have shown behaviors that can suggest a human-like social sense. In recent experiments, dogs have shown that they know to follow a human's pointed finger to find a food treat. Scientists report that this shows dogs are sensitive to human social cues and are able to correctly interpret them. Still, this only proves that dogs know how to find food, not that they have feelings.
Observations of apes have also revealed behavior that appears to represent various human-like impulses. In some tests, chimpanzees demonstrate what looks like altruism helping their own kind and even other species without the expectation of a reward. In the wild, chimpanzee mothers have been observed carrying their dead infants for weeks, appearing to mourn.
Other experiments have cast doubt that animal behavior can reliably signify an underlying feeling. In a recent study, a Barnard College researcher tested dogs to see if their guilty looks were linked to actual bad behavior. Dogs were tempted with a treat and told by their owners not to eat it.