This became evident during some of their first experiments, which were tried on their children and their children's friends. One experiment started as a game. Krause would put the children in groups, then each child would receive tokens that he or she could either keep for themselves or give to the group. Every token donated to the group would result in every person in the group getting one-third of a token. So, sharing a token would mean less for them personally, but more for the group.
Adults have a pretty sophisticated taste for altruism.
For example, when it becomes cheaper to give, they will give more. In another set of experiments, Harbaugh and Krause study children's risk behavior. Others have found that adult women are less willing to take risks than men are. Harbaugh and Krause are interested in what causes this difference and are currently running experiments on entire families to see at what age it develops and whether it runs in families. When they've made their choices, we spin a wheel, and pay the parents in cash and the children in toys.