Karl Marx thought so. In The Economic and Philosophical Manuscripts of 1844, a youthful work that remained unpublished and largely unknown until the mid-twentieth century, Marx describes money as “the universal agent of separation,” because it transforms human characteristics into something else. A man may be ugly, Marx wrote, but if he has money, he can buy for himself “the most beautiful of women.” Without money, presumably, some more positive human qualities would be needed. Money alienates us, Marx thought, from our true human nature and from our fellow human beings.

Marx’s reputation sank once it became evident that he was wrong to predict that a workers revolution would usher in a new era with a better life for everyone. So if we had only his word for the alienating effects of money, we might feel free to dismiss it as an element of a misguided ideology. But research by Kathleen Vohs, Nicole Mead, and Miranda Goode, reported in Science in 2006, suggests that on this point, at least, Marx was onto something.

In a series of experiments, Vohs and her colleagues found ways to get people to think about money without explicitly telling them to do so. They gave some people tasks that involved unscrambling phrases about money. With others, they left piles of Monopoly money nearby. Another group saw a screensaver with various denominations of money. Other people, randomly selected, unscrambled phrases that were not about money, did not see Monopoly money, and saw different screensavers. In each case, those who had been led to think about money – let’s call them “the money group” – behaved differently from those who had not.

When given a difficult task and told that help was available, people in the money group took longer to ask for help.

When asked for help, people in the money group spent less time helping.

When told to move their chair so that they could talk with someone else, people in the money group left a greater distance between chairs.

When asked to choose a leisure activity, people in the money group were more likely to choose an activity that could be enjoyed alone, rather than one that involved others.

Finally, when people in the money group were invited to donate some of the money they had been paid for participation in the experiment, they gave less than those who had not been induced to think about money.

Trivial reminders of money made a surprisingly large difference. For example, where the control group would offer to spend an average of 42 minutes helping someone with a task, those primed to think about money offered only 25 minutes. Similarly, when someone pretending to be another participant in the experiment asked for help, the money group spent only half as much time helping her. When asked to make a donation from their earnings, the money group gave just a little over half as much as the control group.

Why does money makes us less willing to seek or give help, or even to sit close to others? Vohs and her colleagues suggest that as societies began to use money, the necessity of relying on family and friends diminished, and people were able to become more self-sufficient. “In this way,” they conclude, “money enhanced individualism but diminished communal motivations, an effect that is still apparent in people’s responses today.”

That’s not much of an explanation of why being reminded of money should make so much difference to how we behave, given that we all use money everyday. There seems to be something going on here that we still don’t fully understand.

I am not pleading for a return to the simpler days of barter or self-sufficiency. Money enables us to trade – and thus to benefit from each other’s special skills and advantages. Without money, we would be immeasurably poorer, and not only in a financial sense.

But now that we are aware of the isolating power that even the thought of money can have, we can no longer think of money’s role as being entirely neutral. If, for example, a local parents’ organization wants to build a children’s playground, should it ask its members to do the work on a voluntary basis, or should it launch a fundraising campaign so that an outside contractor can be employed?

Harvard economist Roland Fryer’s proposal to pay poor students for doing well at school is another area where using money is open to question. If money were neutral, this would be just a question of whether the benefits of using money outweigh the financial costs. Often, they will – for example, if the parents lack the skills to build a good playground. But it would be a mistake to assume that allowing money to dominate every sphere of life comes without other costs that are difficult to express in financial terms.

Peter Singer is Professor of Bioethics at Princeton University and the author of Animal Liberation, Practical Ethics, and other books. He is currently working on a book about philanthropy and world poverty.