© MPI for Human Cognitive and Brain Sciences
Sharing possessions is an essential theme in every community, but fraught with conflict. A question which remains enigmatic is how and at what stage of development fair sharing occurs spontaneously. Do children suddenly understand what is fair from one day to the next, and then behave accordingly? Or do they simply become better at controlling selfish impulses?
Using game theory, scientists have been studying strategic behaviour in sharing situations. Researchers Nikolaus Steinbeis, Boris Bernhardt and Tania Singer used two of the best-known experiments in this field – the Dictator Game and the Ultimatum Game – with a total of 174 schoolchildren between six and 13 years of age.
In this context, the children were given poker chips which they could later exchange for age-appropriate gifts. First, however, they were asked to share their chips anonymously with another child. In one half of the experiment, during the Dictator Game, the recipient could only passively accept what was given. In the other half, during the Ultimatum Game, there was a veto option: if the recipient did not accept what was offered, both sides left empty-handed. “We were interested in whether the children would share more fairly if their counterparts could reject their offers, and to what extent the strategic adaptation of behaviour is dependent on age and brain development”, explains Nikolaus Steinbeis, lead author of the study.
Sure enough, large differences were detected between the age groups. While most of the older children adapted their behaviour to the respective situation and made fairer offers in the Ultimatum Game, there was little difference between the two situations in the younger group. “Yet this had nothing to do with their intelligence or a lack of fairness understanding”, says Steinbeis. Other factors, such as readiness to take a risk and social competence were also tested for, but were ruled out as possible causes. Instead, a link between strategic behaviour and capacity for impulse control was identified in a further test.
Looking into the brain revealed why impulses were more strongly controlled and children behaved more strategically as their age increased. In this test, 28 children played the Dictator Game and the Ultimatum Game as they lay in a magnetic resonance scanner that measured their brain activity. The older the children were, the more active their lateral prefrontal cortex – a brain area that is among other things, necessary for, controlling one’s own behaviour. Furthermore activity in this region was associated strongly with the degree of strategic behaviour as well as impulse control abilities.
“It is known that full maturity and functional connectivity of the prefrontal cortex is only completed at a late stage of development”, says Nikolaus Steinbeis. Consequently, the fact that children do not share fairly, even when it would be strategically clever to do so should not be attributed to poor understanding of what constitutes a fair split, but to the late maturation of a brain region that is important for impulse control.