Suppose scientists discovered a clump of neurons in the brain that, when stimulated, turned people into egalitarians. This would be good news for Democratic strategists and speechwriters, who could now get to work framing arguments about wealth and taxation in ways that might activate the relevant section of cerebral cortex.

This “share-the-spoils” button has been discovered, in a sense, but it may turn out to be harder to press than Democrats might think.

Pretend you’re a three-year-old, exploring an exciting new room full of toys. You and another child come up to a large machine that has some marbles inside, which you can see. There’s a rope running through the machine and the two ends of the rope hang out of the front, five feet apart. If you or your partner pulls on the rope alone, you just get more rope. But if you both pull at the same time, the rope dislodges some marbles, which you each get to keep. The marbles roll down a chute, and then they divide: one rolls into the cup in front of you, three roll into the cup in front of your partner.

Max Planck Institute for Evolutionary Anthropology

This is the scenario created by developmental psychologists Michael Tomasello and Katharina Hamann at the Max Planck Institute in Leipzig, Germany. In this situation, where both kids have to pull for anyone to get marbles, the children equalize the wealth about 75% of the time, with hardly any conflict. Either the “rich” kid hands over one marble spontaneously or else the “poor” kid asks for one and his request is immediately granted.

But an experiment must have more than one condition, and the experimenters ran two other versions of the study to isolate the active ingredient. What had led to such high rates of sharing, given that three-year-olds are often quite reluctant to share new treasures? Children who took part in the second condition found that the marbles were already waiting for them in the cups when they first walked up to the machine. No work required.

In this condition, it’s finders-keepers. If you have the bad luck to place yourself in front of the cup with one marble, then your partner is very unlikely to offer you one, you’re unlikely to ask, and if you do ask, you’re likely to be rebuffed. Only about 5% of the time did any marbles change hands.

But here’s the most amazing condition — a slight variation that reveals a deep truth. Things start off just as in the first condition: you and your partner see two ropes hanging out of the machine. But as you start tugging it becomes clear that they are two separate ropes. You pull yours, and one marble rolls out into your cup. Your partner pulls the other rope, and is rewarded with three marbles. What happens next?

Max Planck Institute for Evolutionary Anthropology

For the most part, it’s pullers-keepers. Even though you and your partner each did the same work (rope pulling) at more or less the same time, you both know that you didn’t really collaborate to produce the wealth. Only about 30% of the time did the kids work out an equal split. In other words, the “share-the-spoils” button is not pressed by the mere existence of inequality. It is pressed when two or more people collaborated to produce a gain. Once the button is pressed in both brains, both parties willingly and effortlessly share.

Tomasello has found that chimpanzees doing tasks similar to this one do not share the spoils, in any of the conditions. They just grab what they can, regardless of who did what. They don’t seem to keep track of who was on the team. Tomasello believes that the “share-the-spoils” response emerged at some point in the last half-million years, as humans began to forage and hunt cooperatively. Those who had the response could develop stable, ongoing partnerships. They worked together in small teams, which accomplished far more than individuals could on their own.

So now let’s look at a key line in President Obama’s State of the Union address: “we can restore an economy where everyone gets a fair shot, and everyone does their fair share, and everyone plays by the same set of rules.” The president is making three arguments about fairness in this one sentence, but do any of them press the “share-the-spoils” button? If you think that the economy is like a giant marble dispenser with a single rope, then you’d probably agree that if everyone does their “fair share” and pulls on the rope as hard as they can, then everyone is entitled to a “fair share” in the nation’s wealth. But do Americans perceive the economy as a giant collaborative project?

My parents were teenagers in New York City during the Second World War. The home front really was a vast and sustained communal pull. My mother remembers saving up nickels and dimes to buy a war bond. She lingered by her aunts and uncles, waiting for them to finish packs of cigarettes, so that she could grab the foil wrappers for the aluminum recycling campaign.

My parents were part of the generation that went through the depression, a world war, and then the cold war together. This generation accepted federal controls on wages during the war as being necessary for the common good. In the years after the war, the combination of high taxes on top earners, social norms against exorbitant pay, and an increasingly sturdy safety net brought income inequality down from a peak in 1929 to a long valley from the 1950s through the 1970s. It’s a period known as “the great compression.”

The compression went into reverse in the 1980s, and since then, inequality has risen to levels approaching those of 1929. Democrats have long sounded the alarm about rising inequality, but for decades they got little traction among the electorate. It’s only in the last few months, since Occupy Wall Street popularized the concept of the 1 percent, and since we all learned that Mitt Romney pays less than 14% in federal taxes, that the nation’s attention has been focused on the earnings of the super-rich. Will the Democrats’ new emphasis on fairness be enough to rally the nation to raise the top tax rates? Will Obama’s new progressivism press the right moral buttons?

America is in deep fiscal trouble, and things are going to get far worse when the baby boomers retire. Normally, when a nation faces a threat to its very survival, a leader can press the shared-sacrifice button. Churchill offered Britons nothing but “blood, toil, tears and sweat.” John F. Kennedy asked us all to “bear the burden of a long twilight struggle” against communism. These were grand national projects, and everyone was asked to pitch in.

Unfortunately, President Obama promised he would not raise taxes on anyone but the rich. He and other Democrats have also vowed to “protect seniors” from cuts, even though seniors receive the vast majority of entitlement dollars. The president is therefore in the unenviable position of arguing that we’re in big trouble and so a small percentage of people will have to give more, but most people will be protected from sacrifice. This appeal misses the shared-sacrifice button completely. It also fails to push the share-the-spoils button. When people feel that they’re all pulling on different ropes, they don’t feel entitled to a share of other people’s wealth, even when that wealth was acquired by luck.

If the Democrats really want to get moral psychology working for them, I suggest that they focus less on distributive fairness — which is about whether everyone got what they deserved — and more on procedural fairness—which is about whether honest, open and impartial procedures were used to decide who got what. If there’s a problem with the ultra-rich, it’s not that they have too much wealth, it’s that they bought laws that made it easy for them to gain and keep so much more wealth in recent decades.

Sarah Palin gave a speech last September lambasting “crony capitalism,” which she defined as “the collusion of big government and big business and big finance to the detriment of all the rest – to the little guys.” I think that she was on to something and that she was right to include big government along with big business and big finance. The problem isn’t that some kids have many more marbles than others. The problem is that some kids are in cahoots with the experimenters. They get to rig the marble machine before the rest of us have a chance to play with it.

Jonathan Haidt is a professor of psychology at the University of Virginia and a visiting professor at the N.Y.U.-Stern School of Business. He is the author of “The Righteous Mind: Why Good People are Divided by Politics and Religion.”

The research reported on in this article was published in 2011 in Nature, 476, p. 328-331. (Hamann, K., Warneken, F., Greenberg, J. R., & Tomasello, M. Collaboration encourages equal sharing in children but not in chimpanzees.)