They had about two hundred college students play a version of the game known as the Prisoner's Dilemma. The game is based on the tension (紧张气氛) between the interests of an individual and a group. The students played in groups of four. Each player could win points for the group, so they would all gain equally. But each player could also reward or punish each of the other three players, at a cost to the punisher.

　　Harvard researcher David Rand says the most successful behavior proved to be cooperation. The groups that rewarded it the most earned about twice as much in the game as the groups that rewarded it the least. And the more a group punished itself, the lower its earnings were. The group with the most punishment earned twenty­five percent less than the group with the least punishment. The study appeared last month in the journal Science.

　　The other study involved children. It was presented last month in California at a conference on violence and abuse. Researchers used intelligence tests given to two groups. More than eight hundred children aged two to four the first time they were tested. More than seven hundred children aged five to nine.

　　The two groups were retested four years later, and the study compared the results with the first test. Both groups contained children whose parents used physical punishment and children whose parents did not. The study says the IQs — or intelligence quotients — of the younger children who were not spanked were five points higher than those who were. In the older group, the difference was almost three points.

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