What makes one person more generous than another? It could be in the genes

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Kalina Dunne Farrell wrote a note to the tooth fairy last month, asking for extra cash in exchange for a lost tooth so that she could help Syrian refugees.

Kalina, 10, had already amassed her savings from her weekly allowance, and offered to do extra chores, such as scrubbing floors and picking up litter, to earn more. With the $5 windfall she received from the tooth fairy, she gave it all – $157 – to the Ottawa Community Immigrant Services Organization to support its efforts to settle Syrian refugees.

This came as little surprise to her mother. "She's always been like this," Shannan Dunne says, noting that as early as the age of 4, the Ottawa girl was offering to give away her possessions to those less fortunate. "It's in her heart."

And science suggests that it's in her DNA.

For generations, scientists and philosophers have debated what makes people altruistic. As 18th-century poet and satirist Alexander Pope famously wrote: "Many men have been capable of doing a wise thing, more a cunning thing, but very few a generous thing." While it is now understood that generosity is a product of both nature and nurture, researchers are teasing apart just how much of a role genetics play, and how specific gene variations could affect one's willingness to give – whether it's dropping a few coins into a charity box, or grand gestures such as Facebook power couple Mark Zuckerberg and Priscilla Chan vowing this month to dedicate most of their wealth to the public good.

Their quest may lead to insights both practical and philosophical, including how best to encourage charitable giving from those less inclined and why altruism has persisted throughout human evolution. The latter question was said to have confounded Charles Darwin; the selfless behaviour he observed in other species was an ill fit with his theory of evolution by natural selection. Or as University of Guelph associate psychology professor Pat Barclay, whose research focuses on the evolution of human co-operation, says: "Why aren't we totally all selfish psychopaths?"

Ole Pedersen, an immunologist in Denmark whose work revolves around blood banking, was curious to understand the biological influences on why people voluntarily donate blood.

Before the Second World War, biology and heritability were believed to hold the answers to understanding people's motivations and behaviours, Pedersen says, noting that this led to all kinds of dubious and unethical experiments, conducted not only in Nazi Germany but other countries around the world. In the 1920s, for instance, American eugenicist Harry Laughlin used data on U.S. prison populations to indicate an overrepresentation of immigrants, including from Italy, Greece and Eastern Europe, offering his findings as evidence of genetic inferiority.

The postwar era brought a shift toward studying human behaviour through a social-science lens, and in more recent decades – particularly with the mapping of the human genome completed by the Human Genome Project in 2003 – researchers have turned their attention to examining how individuals' biological and genetic makeup interact with environmental factors to explain their motivations and behaviours.

"Nowadays, psychology is very much biology, more or less," Pedersen says.

In a study published this year in the journal Transfusion, Pedersen, a consultant at Naestved Hospital and an associate professor of clinical immunology at the University of Copenhagen, compared the past blood donations of more than 750 twins to test the heritability of giving blood.

He and his research team found that when one twin gave blood, the chances were greater that his or her sibling was also a donor if the two were monozygotic twins – that is, if they are genetically identical – than if they were dizygotic or fraternal.

Using mathematical modelling, the researchers analyzed how much of the subjects' willingness to donate blood was inherited. The result: 50 per cent, Pedersen says, adding the researchers estimate that 30 per cent was explained by sharing a common environment and 20 per cent by random factors or chance.

While he acknowledges the idea of linking altruism to genetics is controversial, Pedersen emphasizes that his study and other altruism research shed light on how genes account for variations in people's generosity, not the presence or absence of their capacity to help others.

"We're not saying that people that don't have the genes for altruism are not altruistic; we're just saying they're less altruistic," he says.

Still, he suggests that blood-donation campaigns may be better able to recruit new donors by targeting families rather than individuals, since relatives of active donors are likelier to give.

At the Hebrew University of Jerusalem, psychology professor Ariel Knafo has homed in on the variants of one specific gene that he believes may affect generosity. In a study published in 2008 in the journal Genes, Brain and Behavior, Knafo and his colleagues analyzed participants' DNA samples for differences in a receptor gene called AVPR1a, which determines one's sensitivity to the hormone arginine vasopressin. Knafo says they targeted this particular gene because previous studies suggest that vasopressin may be related to social behaviour.

"What we showed is that the longer version [of part of a region of the gene called the promoter] is associated with more generosity," Knafo says, explaining that when participants were asked to play a game where they could give away money, "those who had the longer version of the gene were more likely to share with others."

Even so, that does not mean those born with shorter versions are doomed to be tightfisted, nor does it mean people's willingness to share will not fluctuate over their lifetime. Just because a trait may be affected by a certain gene does not mean the trait is fixed, Knafo says. "Genes become sometimes more important or less important depending on the period of life we're in and so on. It's a dynamic system."

To make matters more complex, it appears that generosity involves not just one gene, but a multitude, says associate psychology professor Michael Poulin at the University at Buffalo, who has conducted studies comparing the differences in people's receptor genes for the hormones oxytocin and vasopressin with their willingness to give. "The truth is," he says, "it's probably many, many genes all interacting together that lead to these heritable effects that we see."

Whichever genes may be involved, people who are more generous do seem to enjoy certain advantages that could improve their chances for survival, offering one way in which altruism fits into Darwin's theory of evolution. Prof.Barclay of the University of Guelph says the benefits of helping others can outweigh the costs in the form of "I scratch your back, you scratch my back." That is, whether we consciously seek a payoff or not, we're more likely to receive favours from those we help.

"Our brains and our behaviour have evolved to be adapted on average. Caring for others, wanting to do the right thing, work on average," he says.

Altruism also boosts one's reputation, Barclay explains. When a person is known for helping, others are more likely to want to associate with him or her, whether as friends, business partners or romantic partners.

Barclay found support for this in a study published in 2010 in the British Journal of Psychology, in which he showed that women rated men as more attractive when their dating advertisement profiles indicated that they had altruistic interests, such as volunteer work.

"All else being equal, altruism does seem to increase attractiveness, at least for long-term relationships," he says.

Back in Ottawa, Kalina's mother says she believes that even if altruism is genetic, it needs to be nurtured to flourish. But she says it's hard to say what she has done to encourage her own children's big hearts. The family is not religious, nor have she and her husband ever sat their children down to teach them about giving.

Yet Kalina's brother Callum, 9, shares her generosity. He often asks to buy coffee and muffins for the homeless, and once bought a homeless man some socks and mitts and a hat, and a tin of candy imprinted with "I love you" because, he explained, the man probably did not often get to hear those words.

"It's just what we do," Dunne says. "It's the way we are."