Homo Sapiens evolved evolution wise being an individual ,within a social group.Thus we humans are social species.Much before we could develop language skills due to our larger brain ,we had to communicate in other means and through another ways.One of those ways was observing the behavior on the individual and their facial expressions and body language.Since communication within a group is must, due to its own survival, humans developed the inner skill to do this even subconsciously ,in this way not much of memory or the logical skills get overloaded with with this type of awareness.
Thus ,till this day we instinctively observe and subconsciously read other people emotional states by observing their movement and facial features.It is not a process one is always aware off ,but might become one if you start reading about body language and how the muscles of the face move when a particular emotion/thought is going through your mind(brain).
Having typed that I also would like to mention that humans are also able to feel for their own kind and for other species that they had to look after for their own benefit.Example, for this is how we get sad when we see someone/something in pain or suffering , even when we know this is just a movie.
Overall knowing about others' emotional state by looking at them is skill that has to do more with so called cold reading ,which is natural for us.However feeling someone else's emotions ,without being able to observe his facial expression or body language is example for empathy or intuition.
I feel everyone is empathic to a certain degree though not to the extent those who call themselves empaths are as a true empath can feel the emotions of those around them even if they are attempting to hide their emotions. I for example was recently around someone who was in a very emotional state and honestly started to cry myself yet I'm not a empath. I can't explain why some people seem to be more sensitive to other's emotions than some, but we all have the capability to sympathize with others as human beings and as stated above are very social creatures. Also as previously stated the ability to read emotions based on facial features & other physical signs isn't considered a empathic ability and can even be learned, though I would consider being able to do so naturally a gift. An example of learning such a skill is a trained therapist would likely be able to read a person's posture, stance, and facial features discerning their emotional state in order to better help them especially if they were dealing with someone that was resisting revealing information about their emotional state.
