"We are designed to care about others. The reason we are charitable is that we can't help it, we have a built in brain mechanism that connects us to other people."
Brown calls this brain mechanism the "care giving system."
"When people give out of compassion or because they really care about someone, there is a biological system at its roots," she explained. "There is a neurohormonal mechanism in the brain that exists because of a need to raise helpless offspring."
And it is this care giving system that oxytocin appears to affect. Oxytocin is a chemical that facilitates social interactions and bonding with our spouses and children. Previous studies have shown it may also be involved in trust.
Zak proposes that oxytocin cranks up the empathy and attachment we feel toward others. When we are more empathetic, we become more generous -- which explains why participants infused with the hormone gave away more of their money.
Brown agrees. "There are hormones, including oxytocin, that motivate us to suppress immediate short-term interests to take care of someone else," she said.
"It's obvious that people are all over the map when it comes to generosity -- some people are quite generous, others, not so much," said Bill Harbaugh, an associate professor of economics at the University of Oregon.
"Previous studies to understand this have focused on easily observable characteristics like gender, age, and religiosity. This paper provides a way to understand the biological and chemical foundations of the differences that we all observe in everyday life."
Of course, outside of the lab, people are not inhaling oxytocin. Our bodies make this hormone, which means further research is needed to determine how natural levels of oxytocin affect generosity.
"What this important paper does is reveal a chemical pathway that alters generosity," said Harbaugh. "So to understand why people give, we need to understand the factors that determine the production and uptake of oxytocin. How much of this is genetic, how much of it is acquired, and what are the interactions?"
And whether or not generosity is innate or acquired, writing that check to charity or volunteering your time at the soup kitchen may pay off in the long run.
"People who behave more empathetically tend to be happier, live longer, and are less sick," said Zak. "Social connections are associated with a longer, healthier life.
"Although it might be monetarily costly to be generous in the short run, there are long-term health benefits."