When a baby cries, it could be hungry, tired, hot or, as new research suggests, jealous.
Babies can show signs of jealousy when they're as young as three months old, new Canadian research has found, which contradicts theories that it takes two years for humans to first experience the emotion.
Researchers at York University's psychology department found that babies have negative reactions when their mother's attention is diverted by another person.
The team, led by professor Maria Legerstee, studied babies who were three, six and nine months old.
When a female researcher sat near the babies, the infants didn't seem to mind if the researcher seemed too busy to communicate with them.
However, if the researcher engaged in a conversation with the babies' mothers, they "kicked their legs, yelled out loud and turned in their seats," Legerstee said in a statement. "I've never seen anything like it."
Legerstee's findings will appear in a book to be published next fall entitled "Handbook of Jealousy: Theories, Principles and Multidisciplinary Approaches."
Jealousy, along with embarrassment, pride and guilt, are so-called non-basic emotions, which researchers have long thought only developed during the second year of life because they are too complex for infants' basic cognitive abilities.
"Jealousy implies the formation of a social bond, and is a reaction to the presence of one who threatens this bond," Legerstee said. "Thus at three months infants are aware of other people. This is strong evidence that infants understand that motives or goals guide our communicative behaviour."
