Source: http://www.smithsonianmag.com/science-na...

After training the dogs with one familiar face, the researchers found that their subjects had little difficulty applying what they learned—the universal signs of human happiness or anger—to photos of faces they had never seen before. The team noted, however, that dogs were slower to correctly select the angry faces, perhaps a sign that the canines could already associate mad-looking expressions with bad outcomes and thus wanted to avoid those faces.

As far as the authors know, this is the first time researchers have shown that one animal species can recognize the emotional state of another (humans recognizing emotions in animals doesn’t count). The team points out, though, that it would come as no surprise if other animals have similar powers of interspecies communication, since the information offered by facial expressions could be handy for survival. A lioness recognizing whether a wildebeest is preparing to angrily charge or to flee just by regarding the squint of its eyes and flare of its nostrils could mean the difference between a mortal injury and dinner.   

Before the authors delve into the greater animal kingdom, though, they plan to further explore their canine findings. Experiments with puppies could lend insight into whether facial expression recognition is something dogs learn over their lives or if it's something more innate. And trials with wolves could indicate whether human breeders bestowed emotion recognition in their canine companions via artificial selection, or whether that trait was something dogs’ ancient relatives developed on their own simply by living in the vicinity of humans.

While the initial controlled laboratory findings don’t prove that your dog is watching your every facial move for clues about how you are feeling, they do open up the possibility that dogs are even more empathetic best friends than we thought.