Fleur went through a fairness phase. It especially escalated around age two where she would express displeasure about unfair treatment. I have no doubt her like and dislike of daycare adults is based on her perception of their being fair. She is getting better about expressing that position. But, I would agree she has been evaluating this since around a year old.
The results suggest that toddlers reward those who are acting fairly, adding to the evidence that very young children have a strong sense of what is “right” or normative. But, interestingly, these kids don’t seem to punish those who have been unfair (in fact, the researchers suggest that the children instead tended to avoid making responses towards unfair distributors, as they touched the screen fewer times overall after seeing those who acted unfairly).
At Just 16 Months Old, Toddlers Will Reward Someone For Acting Fairly
Lots of ideas about evolution suggest the human brain is geared towards communication. However, I would suggest that brain power is about evaluating fairness. People suck at mathematics and logic until it deals with fairness for themselves. Communication is also about fairness in that we talk and write to establish common ideas upon which to make judgements.
Polymath Parent 