In a fascinating study entitled "Induction of empathy by the smell of anxiety," published in the journal of the Public Library of Science (PLoS) in 2009, researchers discovered "The chemosensory perception of human anxiety seems to automatically recruit empathy-related resources." Smelling chemical signals from the sweat of anxious subjects elicited an empathic response, even when the smell was below the threshold of consciousness in half the subjects.
Empathy, in fact, has concrete and measurable therapeutic effects in others. In 2009, researchers found that practitioner empathy reduced the duration of the common cold in their patients. Conversely, a negative and/or indifferent attitude towards the patient has measurable adverse effects, also known as the nocebo effect.
Given that many believe empathy is not "hard-wired" into us, but rather represents a "higher faculty" in constant struggle with our "baser," fundamentally selfish instincts, this new research is all the more encouraging. Perhaps in light of it, it will be easier for those who do not experience compassion directly or often enough, either on the giving or receiving end, to come to appreciate its essential role in our past, present and future.
Comment: By the same token, the same odor might attract a psychopath to his prey.