From the New Scientist: researchers studied the facial expressions of 21 people who were born blind, and found they were “significantly more likely to make angry, sad and pensive facial expressions that resembled those of their relatives than of strangers.”

I guess it can be attributed to similarities in the musculature of the face. OTOH for three of the facial expressions studied, “joy, surprise and disgust” “the resemblance to relatives and strangers was not significantly different.”

One of the researchers speculates that this “might be because these emotions are for some reason more universally similar and not as prone to genetic variations.”