Researchers at the University of Toronto asked college students to shop online for products at either an eco-friendly or a normal store. When asked afterwards to divide a small amount of money between themselves and a stranger, those who went the eco route gave less to the stranger:

“When we engage in a good deed, that gives us a kind of satisfaction,” says Nina Mazar, professor of market­ing and a co-author of the paper. With that self-satisfied feeling can come tacit permission to behave more sel­fishly next time we have the oppor­tunity, Mazar says. Previous research has documented this licensing effect in other contexts; a study published last year revealed that asking people to ruminate on their humanitarian qualities actually reduced their char­itable giving.

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