From The Atlantic:
Conventional scientific wisdom recognizes six “classic” emotions: happy, surprised, afraid, disgusted, angry, and sad. But the [University of Glasgow] scientists studied people’s facial expressions, and the emotions they signal, by showing people computer-generated facial animations. They asked the observers to characterize the faces based on those six basic emotions, and found that anger and disgust looked very similar to the observers in the early stages, as did fear and surprise. For example, both anger and disgust share a wrinkled nose, and both surprise and fear share raised eyebrows.
The thing was, as time went on, the face showed the distinction between the two, but when the emotion first hit, the face signals are very similar, suggesting, the researchers say, that the distinction between anger and disgust and between surprise and fear, is socially, not biologically based.
This leaves us with four “basic” emotions, according to this study: happy, sad, afraid/surprised, and angry/disgusted. These, the researchers say, are our biologically based facial signals—though distinctions exist between surprise and fear and between anger and disgust, the experiment suggests that these differences developed later, more for social reasons than survival ones.
“These results show that dynamic facial expression models transmit an evolving hierarchy of signals over time, characterized by simpler, biologically rooted signals early in the signaling dynamics followed by more complex socially speciﬁc signals that ﬁnely discriminate the six facial expressions of emotion,” the study reads.
The researchers posit that the wide-open eyes that come with fear/surprise are a response to “fast-approaching” danger, and that we widen our eyes to get more visual information. The wrinkled nose that comes with anger/disgust, they say, is a response to “stationary danger,” such as pathogens—by wrinkling your nose, you may be less likely to breathe in something harmful.
“Our data reﬂect that the six basic facial expressions of emotion, like languages, are likely to represent a more complex set of modern signals and categories evolved from a simpler system of communication in early man developed to subserve developing social interaction needs,” the authors wrote. By that they mean these four emotions are the basic building blocks from which we develop our modern, complex, emotional stews.
It’s remarkable how so many seemingly mundane characteristics of our species have vital evolutionary origins for our survival.