Why do our facial expressions change so much with various emotions? It's all rooted in our need to see and interpret what's happening around us, say researchers from Cornell University.

For instance, people's eyes widen in fear, boosting sensitivity and expanding their field of vision to locate danger. Then again, when folks are repulsed by something, their eyes grow more narrow, in order to block out light and sharpen focus on the source of their disgust.

The findings, published in the Mar. 2014 issue of Psychological Science, suggest human facial expressions originated as adaptive reactions to environmental stimuli -- and were not initially used as forms of social communication signals, Adam Anderson, professor of human development in Cornell's College of Human Ecology, said in a new release.

The research offers validation to Charles Darwin's 19th century theories on the evolution of emotion, asserted Anderson, the research paper's senior author.

"These opposing functions of eye widening and narrowing, which mirror that of pupil dilation and constriction, might be the primitive origins for the expressive capacity of the face," said Anderson. "And these actions are not likely restricted to disgust and fear, as we know that these movements play a large part in how perhaps all expressions differ, including surprise, anger and even happiness."

In addition, he said, emotions filter our reality, shaping what we see before light ever reaches the inner eye. "We tend to think of perception as something that happens after an image is received by the brain, but in fact emotions influence vision at the very earliest moments of visual encoding."

Anderson's Affect and Cognition Laboratory has now moved forward to study how contrasting eye movements may explain how facial expressions have evolved to support nonverbal communication across cultures.

"We are seeking to understand how these expressions have come to communicate emotions to others," Anderson said. "We know that the eyes can be a powerful basis for reading what people are thinking and feeling, and we might have a partial answer to why that is."