So Messrs Maude, Hunt and Willetts think "it's startling that the richest third of donors in Britain give less, as a proportion of their income, to charity than the poorest third." I suppose the Tory doyens have been a bit busy of late to be browsing the current psychology journals, but had they done so, they might not have been quite so surprised.

Michael W Kraus, of the University of California, San Francisco, is one of a number of social psychologists who have recently been busy demonstrating that lower socioeconomic status (SES) is intricately linked to all sorts of prosocial behaviours. Everything else equal, the less wealth, education and employment status we have, the more charitable, generous, trusting and helpful we appear to become. In interactions with strangers, poorer people are more likely to use polite, attentive, respectful gestures. Most recently, in a paper just published in the prestigious journal Psychological Science, Kraus et al report that lower SES subjects show significantly greater empathy than their richer, better educated counterparts. He argues that this tendency to empathise may at least partly explain the other observations of prosocial behaviour.

The tests used in the latest experiments recorded subjects' ability to read emotions in the faces of others, which is considered a reliable signifier of broader empathic skills. As expected, using both pictures and human interactions, SES was inversely correlated with empathic accuracy. Empathic emotions are central to compassionate and prosocial tendencies, and Kraus argues that these cognitive processes are necessary for survival; human beings who find themselves in a high-status position are more likely to believe that they can control their own destinies, able to use their power, authority or wealth independently to keep themselves safe and secure. Those further down the social pecking order are more vulnerable, and so more likely to need to co-operate to survive.

Are these simply learned social mores? Or could it be that the rude, heartless and selfish have a natural advantage in getting ahead in this world? It seems not. In the key experiment, Kraus manipulated people's own perceptions of their social status by getting them to visualise interactions with people either far above or far below their own status (such as Bill Gates, or a homeless man) before conducting the empathic accuracy test. He found that those who had been manipulated into thinking themselves relatively lower class performed significantly better than the other group. This suggests that far from being fixed, innate or learned, empathic abilities are effectively switched on or off involuntarily, according to context. When we begin to feel superior, we simultaneously become less empathic.

Notwithstanding the usual caveats surrounding a single experiment, or the perils of extrapolating from the psychology laboratory to the complexities of the real world, this is an authoritative study which deserves to be taken seriously. If it proves robust, it is a remarkable finding with some serious implications.

On a personal level, it offers gratifying validation for my long-held belief that the movie classic Trading Places is the definitive text on social psychology. Beyond that, if left/right politics are at least partly dependant on social collectivism as opposed to individualism, this may help to explain the middle-class phenomenon of rightward drift through the decades. Perhaps we don't tend to become more rightwing as we grow older, but we grow more rightwing as and when we move up the socioeconomic hierarchy.

At an interpersonal level, this has relevance to everyone from marriage counsellors to management consultants. Have you ever had a kind, thoughtful colleague who turns into a monster the day after a promotion? This might tell you why.

In the light of the recent debates on gender and science, this experiment may even throw a new twist into the mix. To what extent has women's historical role as nurturers and carers been not just a cause of their lower social status relative to men, but also a consequence of it? If so, might some loss of female empathy be a price that has to be paid for social equality?

Most immediately, these findings should help to persuade the three wise monkeys of the "big society" that the philanthropy of the wealthiest should never be taken for granted. If their hopes for the fabric of the nation rest to any extent upon the compassion and generosity of the most wealthy and powerful, they may have a few more startling surprises in store.