Whether or not humans are the only empathic beings is still under debate. In a new study, researchers directly compared the 'yawn contagion' effect between humans and bonobos (our closest evolutionary cousins). By doing so they were able to directly compare the empathic abilities of ourselves with another species, and found that a close relationship between individuals is more important to their empathic response than the fact that individuals might be from the same species.
The ability to experience others' emotions is hard to quantify in any species, and, as a result, it is difficult to measure empathy in an objective way. The transmission of a feeling from one individual to another, something known as 'emotional contagion,' is the most basic form of empathy. Feelings are disclosed by facial expressions (for example sorrow, pain, happiness or tiredness), and these feelings can travel from an "emitting face" to a "receiving face." Upon receipt, the mirroring of facial expressions evokes in the receiver an emotion similar to the emotion experienced by the sender.