In the experiment, volunteers reported their own level of happiness after each act of generosity.
If we assume that human behavior is motivated primarily by self-interest, it seems illogical to voluntarily sacrifice resources for others.
In attempting to resolve this paradox, some scholars have formulated the theory that giving or giving satisfies the desire to elevate the position of the individual in a group.
Others have suggested that the act promotes tribal cooperation and cohesion - a key element in the survival of mammals. Another explanation is that we donate just because we expect to receive something in return.
A study published on Tuesday suggests that the answer can be much simpler: giving leaves us happy.
The scientists conducted an experiment in a laboratory in Zurich, Switzerland, with 50 people who reported their own levels of happiness after acts of generosity. Consistently, they indicated that giving was an experience of well-being.
Brain image
At the same time, MRIs revealed that an area of the brain linked to generosity triggered an otherwise happiness-related response.
"Our study provides behavioral and neural evidence that supports the link between generosity and happiness," the team wrote in the journal Nature Communications.
The researchers informed participants that each would have at their disposal 25 Swiss francs ($ 26) a week for four weeks.
Half the participants were asked to commit to spending money on others, while the rest could plan how they would spend the money on themselves. No money was actually received or spent by either group.
After committing themselves to the expenses, participants answered the questions while their brains were being examined. The questions evoked scenarios that pitted the participants' own interests against the interests of the recipients of their experimental generosity.
Researchers examined activity in three areas of the brain - one linked to altruism and social behavior, a second to happiness, and a third area involved in decision making.
The team found that the group that pledged to donate money reported being happier than those who were going to spend the amount on their own.
The findings have implications for education, politics, economics and public health, according to the researchers. "Generosity and happiness enhance individual well-being and can facilitate social success," they wrote.