Have you given money to Haiti yet? If you haven t, why not? And perhaps a more puzzling question: If you have given money in the wake of Tuesday s devastating earthquake, the death toll of which may climb into the hundreds of thousands, what exactly motivated you to do that?

The latter question may seem dumb, even callous. You gave, it s obvious, because you re an altruistic person, you have compassion for the victims, and it s the moral thing to do. But, in truth, donating to charity is a wholly irrational act, economically speaking: It doesn t benefit you and, in fact, it leaves you poorer by precisely the amount you donate (save tax deductions). Whatever s behind the impulse to give to charity, the one thing it s not is obvious.

As economists and social scientists have begun to dig around in recent decades into people s true motives when they give to charity, what they ve found hasn t exactly been in keeping with the flattering way we humans like to see ourselves. While altruism may play its part, there are also many other factors at play when we donate: guilt, the desire to boost our social status, the need to feel good about ourselves, even our sex drives. Any attempt to understand why we give or to get us to give more must deal with this dirty and tangled reality.

The first thing to understand about our charitable impulses is that they re one of the least rational facets of our economic being. Not only is giving away money for no obvious benefit irrational, but the way we give away money is extremely strange and that strangeness is where we can glean insight into our true motives.

Take, for instance, the problem of bigness. The bigger the problem, generally speaking, the more money is needed to solve it. Unfortunately, the more overwhelming a problem is, the more abstract it is, the more our brains shut down.

University of Oregon psychology professor Paul Slovic, a pioneer in charity research, took a look at this problem recently in a clever experiment. Taking people who had just participated in a paid psychology study, he gave them the chance to donate up to $5 of their earnings to the charity Save the Children. When one group was shown a picture of a malnourished 7-year-old African girl named Rokia, they donated generously. But when another group was shown the picture of Rokia and informed about the larger problem of millions of children in need, they donated roughly half as much as the picture-only group.

What really moves people is making an emotional connection, Slovic said. The numbers not only don t convey feeling, they actually get in the way of feeling. While what s been called psychic numbing can have beneficial effects the term was coined to describe how rescue workers turned off their emotions to deal with the horrific aftermath of the Hiroshima bombing, and relief workers are presumably operating off of the same thing in Haiti today it also gets in the way of people watching from abroad reacting compassionately.

By necessity, our well of compassion is far from bottomless. The current view is that altruism, to the extent it exists in any pure form in the human animal, is an evolutionary adaptation to bind families and small communities. And, as ancient as these preferences may be, our contemporary giving habits seem to reflect little change. Roughly 80% of Americans giving, according to the Center on Philanthropy at Indiana University, is focused on their local communities and churches. In 2004, according to a report by the Center, international aid received just 1% of household giving; tsunami relief got another 2% of the pie that year.

So, when and why do we give?

We give when it can help us directly. Some giving is quite self-centered. Alumni giving, to take one example, has been found to correlate in size and frequency to a less-than-shocking variable: the age of one s child and the likelihood of his or her applying to the school in question.

We give when it can help us indirectly, by raising our social status helping us appear wealthy or generous. In another study on alumni giving, Yale economist Dan Karlan found (in a paper delightfully titled, Hey Look at Me ) that individuals were more likely to give when offered public recognition in a newsletter and that they were more likely to donate at a higher level if informed that donors would be separated into giving circles based on the amount given. While we may not want to believe that we donate to charity for recognition and social status, empirical research has found that anonymous donations are exceedingly rare (perhaps as low as 1% of all donations) even though they re eligible for the same tax treatment as other donations.

We give to feel good. One way we know this is indirectly: by the fact that people seem to give to charity with little to no regard for the effectiveness of their donations. We also have some direct evidence: Recent brain imaging studies have shed light on the theory that we get a warm glow from giving to charity. In one specific study, giving money to a food bank activated some of the same brain areas activated by rewards such as receiving food or money.

We give to alleviate guilt and repair our self-image. In a recent column I discussed how when people focused on good things about themselves, they felt less need to engage in good deeds, such as donating to charity. Well, the flip side of that same experiment where people wrote positive or negative essays about themselves and then were asked to donate up to $10 to a charity of their choice is that the people who focused on the bad things about themselves donated five times more than those who wrote about their positive traits. As the study s authors put it, when moral identity is threatened, moral behavior is a means to regain some lost self-worth.

We give when it can increase our odds with the opposite sex. In another experiment, by University of Chicago economist John List, a team tested the effectiveness of various door-to-door fundraising techniques. One technique that had tremendous success: turning up the hotness of the woman who asked for money ( a one-standard deviation increase in physical attractiveness, in scientific lingo). This increased average donations by 50% to 135%. As the paper delicately puts it: This result is largely driven by increased participation rates among households where a male answered the door.

People generally want to do good for their fellow man, even if their motives are necessarily human and mixed. But crises like tsunamis, hurricanes and earthquakes numb us out of psychological necessity to the scale of suffering involved.

Stories, not numbers. Recognition, not anonymity. Feedback. Affirmation. Inducing a little guilt. Heck, even hiring a pretty face. Any one of these tools can help leverage more cash in a crisis. A social-network campaign operating on some of these principles where people can text HAITI to 90999 to donate $10 to the Red Cross had already raised an unprecedented $5 million for relief efforts, as of Thursday afternoon.

The science has given us the theories. The technology has given us the equipment. The time for experimentation is now.

Ryan Sager writes the blog Neuroworld at TrueSlant.com.