"At the very bottom, our concern for image management and reputation is about the fear of rejection, one of the main engines of the human psyche."
The rise of social media has made it clearer how adults feel about their image. People report feeling crushed if a post does not receive sufficient "likes", while psychologists have coined the condition "Snapchat dysmorphia" for users who become so obsessed with enhanced digital versions of themselves that they become depressed by reality.
To test how early social anxiety emerges, scientists carried out several experiments involving 144 children between the ages of 14 months and 24 months, using a remote-control robot.
A researcher either watched the youngster playing with the robot, or turned away and pretended to read. When the child was being watched, they showed more inhibition and embarrassment than when the researcher was not watching.
In a second experiment, the researcher used two different remote controls when demonstrating the toy, saying, "Wow! Isn't that great?" with the first and "Uh-oh! Oops, oh no!" with the second. They found children used the remote control associated with the negative response more when not being watched, choosing the positive one when under the gaze of the researcher.
Youngsters were then shown the toy being operated by two researchers, one who said, "Yay! The toy moved!" and one who frowned and said, "Yuck! The toy moved!"
When the child was invited to play they were much more likely to press the remote when the researcher who gave a positive response was watching.
"We've shown that by the age of 24 months, children are not only aware that other people may be evaluating them, but will alter their behaviour to seek a positive response," said doctoral student Sara Valencia Botto, first author of the study.
"This behaviour is like older children who behave well and do good things while others are watching and misbehave when no one is paying attention.
"Our concern for reputation is something that defines us as human."
Previous research found the same behaviour by the time a child reached four years old, but the latest study suggests it emerges far earlier.