Do humans have a "goodness gene?" Is there something inside us that genetically pushes us to reach out to the people who were devastated by the tsunami that struck southern Asia? Or do we do it because we have seen others suffer, and our culture has taught us the meaning of social responsibility?
The old "nature vs. nurture" debate just won't go away, as revealed by a number of studies in recent scientific journals and the sometimes nasty debates that follow.
Over the years the pendulum has swung back and forth between two extreme positions. Either we are what our genes tell us to be. Or we are what our culture has taught us to be.
The truth certainly lies somewhere in between, with opinions ranging all the way from "genetic determinism," in which genes are everything, to "free will," in which we have the freedom to shape our own sense of social responsibility regardless of our genetic composition.
It's a tough nut to crack, because it wouldn't be socially responsible to manipulate some human lives from the moment of birth, controlling everything in their environment, so that we can separate cultural factors from genetics.
Some scientists believe an alternative is right in front of us, and it doesn't require any manipulation of human lives to shed some light on this difficult subject. Identical twins, they say, provide that window.
If genetics plays a significant role in determining whether we are socially responsible, for example, then identical twins should agree with each other more often than the rest of us, even fraternal twins, because the genes they share are encoded with the difference between right and wrong.
Following that line of thought, researchers have found all kinds of evidence of genetic determinism, ranging widely from violence to forgiveness.
Interestingly, nearly all of those studies have focused on negatives, like a propensity to commit acts of violence.
"We take good behavior for granted," says psychologist Philippe Ruston of the University of Western Ontario in London, Ontario, author of a recent study on the genetic basis for altruism. "We almost think of it as the norm. So we're looking at deviations from our socially responsible norms."
In his most recent research, Ruston wanted to know if there is a genetic component to good behavior. In other words, do we have a "goodness gene" that encourages us to do the right thing?
Ruston thinks the answer is yes, although such a gene is obviously expressed differently in some persons than it is in others.
He bases that opinion on decades of analyzing data he collected through the University of London Institute of Psychiatry Adult Twin Register, the source for many studies about twins and genetics.
Ruston submitted a series of 22 questions to 174 pairs of identical twins, who share all their genes because they came from a single egg, and 148 pairs of fraternal twins, who share only half their genes because they came equally from the mother and the father. He wasn't particularly interested in the genes that determine our species, because we all share nearly all those genes, but in the "segregating genes," or those that differ from one person to the next because of inheritable traits.
We all have genes that cause us to have two eyes, for example, but segregating genes, which differ even among fraternal twins, determine the color. But even the segregating genes are the same in identical twins, Ruston says.
So identical twins should agree on moral issues twice as often as fraternal twins, at least if genetics has any influence on human compassion.
And, he says, that's precisely what he found.
The participants used a scale of 1 (strongly disagree) to 5 (strongly agree) to evaluate a number of statements, including "Cheating on income tax is as bad as stealing" and "I am a person people can count on."
The answers among identical twins were almost twice as alike as among the fraternal twins, leading Ruston to conclude that genes account for 42 percent of the individual differences in attitudes.
Not everybody will buy that, of course. Paul R. Ehrlich of Stanford University, a leading proponent of the "environment is everything" school of thought, maintains that identical twins have very different life experiences than the rest of us. Even parents sometimes have trouble telling them apart, so their environmental experiences may be more similar than different.
"Genetic evolution did not determine most of how we act or provide us all with a pre-programmed 'human nature,' " Ehrlich told a meeting of the American Institute of Biological Sciences. "There is no reason to believe that human beings are either innately violent or innately peaceful, instinctively disposed to wreck their environments or to be conservationists, or born genetically gay or genetically straight."
"That's silly," Ruston says. The vast majority of scientists in the field believe genes do play a role, he adds.
"It's both," he says. "The genes tell us that some of us are a tad more socially responsive than are others."
That's likely true, even on a gender level, he adds. One of the questions he asked the participants was whether they liked seeing others open presents. A hardy yes means the person is empathetic.
"Females are much higher on that," Ruston says. "In fact, I didn't find a single female in my sample who didn't endorse that item. But 20 percent of males will say 'nope,' they're not interested in watching people open presents."
Lee Dye's column appears weekly on ABCNEWS.com. A former science writer for the Los Angeles Times, he now lives in Juneau, Alaska.