By Caroline Wilbert
WebMD Health News Reviewed by Louise Chang, MD

Aug. 27, 2008 -- Three- and 4-year-olds are selfish and not likely to share -- hardly news to any parent who has presided over a toddler play date. The good news is children do develop altruism and the desire for things to be fair by the time they are 7 or 8, according to a Swiss study.

The study, led by Ernst Fehr at the University of Zurich and published in Nature, is based on research done with 229 Swiss children. The study delves deeply into when children learn to share, at what age equality becomes important to them, whether they are more willing to share with kids they know than with strangers, and how birth order affects a child's willingness to share.

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For the study, children were offered candy and choices in several scenarios.

In a scenario called the sharing treatment, the child was offered two choices. Choice No. 1: one piece of candy for himself or herself and one piece of candy for another child. Choice No. 2: two pieces for himself or herself, and nothing for the other child.

At age 3 and 4, only 8.7% of children in the sharing treatment chose to give another child they knew one of the pieces of candy. By age 7 and 8, 45% of children chose to share one of the candies. In general, older children chose more consistently egalitarian outcomes in all the scenarios, according to researchers. They were more likely to want everything to be fair.

For instance, in a scenario called the envy treatment, when the child could choose one for himself and one for his partner or one for himself and two for his partner, the older child was more likely to decide everyone should get just one candy.

The study also says that as children become more egalitarian, they also become more parochial. In some cases, the children were paired with kids from their schools, while sometimes they were paired with kids they did not know. At all ages, children were more likely to share with children they knew, but that tendency increased with age.

Researchers also sliced and diced their data by birth order. Children who didn't have siblings were more likely to share than children with siblings. The least likely to share? Youngest children.

The researchers argue that studying the development of egalitarianism and parochialism -- and their possible connection -- is important to understanding the evolution of humans. "These results indicate that human egalitarianism and parochialism have deep developmental roots, and the simultaneous emergence of altruistic sharing and parochialism during childhood is intriguing in view of recent evolutionary theories which predict that the same evolutionary process jointly drives both human altruism and parochialism," the researchers write.

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