When do we start to be aware of fairness?

Imagine a day in the African savanna, when you killed a lion, and went back to your tribe; the chief offered to distribute the lion to everyone with equal shares, but you rejected it because you felt it was unfair to you, and no one had his share. In another day, your brother came back with a dead lion, and the chief offered to give you half of the lion even though you did nothing for the hunting, you rejected again because you felt it was unfair to your brother, and no one got his share. We all have the sense of fairness, which is important for human cooperation.

In economics, this phenomenon is called inequity aversion — disadvantageous inequity aversion (DI) for the first case, and advantageous inequity aversion (AI) for the second case. So when do we start to have the sense of fairness as we grow up? Do we share different fairness in different cultures?

A recent paper in Nature reported the investigation of these questions in children of 4-15 years old from seven communities, with two in WIERD (Western, industrialized, educated, rich, and democratic) countries (USA, Canada), and five in non-WIERD countries (India, Mexico, Peru, Senegal, Uganda). 

They hypothesized that DI is more common than AI across cultures; Children in WEIRD communities are more likely to show AI than those in other communities do, given the difference on adhering to norms of equality; and DI appears earlier than AI. 

To test the hypothesis, they used inequity game in 866 pairs of children, with one of them as actor to decide accepting or rejecting the offers from the experimenter. The offers are small food treats distributed at 1-1 (equal), 1-4 (DI), or 4-1 (AI) ratios. 

They did prove their hypothesis though with some exceptions. What does it mean? They explained, DI "may represent an early application of norms of fairness with a focus on unfairness to oneself... or preserve one’s status relative to potential competitors". Whereas AI "express a norm-based sense of fairness with a focus on unfairness to others". Its commonness in WIERD countries may be due to their incline of adhering to norms of equality.

What's next? Like the authors suggested, they will do more experiments with more life span, diverse communities, and affecting factors of AI and DI. 

Although it's interesting, how will this help in economy? It seems you need both DI and AI to keep the society running normally. Isn't it natural for the survival game?