Evolution reaches across time and face
Timing is indeed crucial, with a new paper finding time is the difference between fear and surprise in facial expressions.
A recent study has found a possible evolutionary basis for the timing of our facial expressions.
It has shown that the face communicates important information first, while more complex facial messages take a little while.
The conclusion was reached by researchers at the University of Glasgow, who were studying the range of different muscles within the face (referred to by researchers as ‘Action Units’) involved in signalling different emotions, as well as the time-frame over which each muscle was activated.
This is the first study to add the aspect of time, or ‘temporal dynamics’, to the assessment of facial expressions.
The team claims that while expressions of happiness and sadness are clearly distinct across time, fear and surprise share a common signal – wide open eyes – early in the signalling dynamics.
Similarly, anger and disgust share a wrinkled nose.
It is believed that these early signals could represent more basic danger signals.
Later in the signalling dynamics, facial expressions transmit signals that distinguish a larger array of reactions and emotions.
Lead researcher Dr Rachael Jack said: “Our results are consistent with evolutionary predictions, where signals are designed by both biological and social evolutionary pressures to optimise their function.
“First, early danger signals confer the best advantages to others by enabling the fastest escape.
“Secondly, physiological advantages for the expresser – the wrinkled nose prevents inspiration of potentially harmful particles, whereas widened eyes increases intake of visual information useful for escape – are enhanced when the face movements are made early,” she said.
“What our research shows is that not all facial muscles appear simultaneously during facial expressions, but rather develop over time supporting a hierarchical biologically-basic to socially-specific information over time.”
The findings challenge the common notion that facial expressions are limited to six stagnant forms.
“Our research questions the notion that human emotion communication comprises six basic, psychologically irreducible categories. Instead we suggest there are four basic expressions of emotion,” Dr Jack said.
“We show that ‘basic’ facial expression signals are perceptually segmented across time and follow an evolving hierarchy of signals over time – from the biologically-rooted basic signals to more complex socially-specific signals.
“Over time, and as humans migrated across the globe, socioecological diversity probably further specialised once-common facial expressions, altering the number, variety and form of signals across cultures,” she said.