Recent study reveals how fear and other human expressions evolved and then come to signal a person's feelings to the people around him.
The basic idea, according to Azim F. Shariff of the University of Oregon, is that the specific facial expressions associated with each particular emotion evolved for some reason.
Shariff cowrote the paper with Jessica L. Tracy of the University of British Columbia.
Fear helps respond to threat, and the squinched-up nose and mouth of disgust make it harder for you to inhale anything poisonous drifting on the breeze. The outthrust chest of pride increases both testosterone production and lung capacity so you're ready to take on anyone.
Then, as social living became more important to the evolutionary success of certain species, most notably humans, the expressions evolved to serve a social role as well, so a happy face, for example, communicates a lack of threat and an ashamed face communicates your desire to appease.
According to Shariff, the research is based in part on work from the last several decades showing that some emotional expressions are universal, even in remote areas with no exposure to Western media, people know what a scared face and a sad face look like.
This type of evidence makes it unlikely that expressions were social constructs, invented in Western Europe, which then spread to the rest of the world.
It's not just across cultures, but across species.
"We seem to share a number of similar expressions, including pride, with chimpanzees and other apes," Shariff said.
The theory that emotional facial expressions evolved as a physiological part of the response to a particular situation has been somewhat controversial in psychology, another article in the same issue of Current Directions in Psychological Science argues that the evidence on how emotions evolved is not conclusive.
Shariff and Tracy agree that more research is needed to support some of their claims, but that,
"A lot of what we're proposing here would not be all that controversial to other biologists.
"The specific concepts of 'exaptation' and 'ritualization' that we discuss are quite common when discussing the evolution of non-human animals," Shariff added.
The study has been published in Current Directions in Psychological Science.