If you've been planning a shopping trip with the kids for bank holiday Monday, you might not want to read any further, because teaching your children consumerism is helping to turn them into selfish, immoral creatures without a streak of empathy, according to a new study. You may be making them just like stressed-out adults, whose potential as human beings is killed off as genuine altruism is suffocated by their greed and anxiety.

In a new book which suggests that social changes and the shift towards an ever more unequal society are making us cold-hearted and mean, psychotherapist Graham Music says we're more likely to be born big-hearted and kind but then pushed towards being selfish and cold than the other way around.

"We're losing empathy and compassion in dealing with other people in our society," said Music, a consultant child and adolescent psychotherapist at the Tavistock and Portman clinics in London. "There is a lot of evidence that the speed of life and the resultant anxiety have an enormous impact on how we deal with other people. We all know it anecdotally. You live in a dog-eat-dog world and it makes sense to be highly stressed and vigilant to cope with it. From that stress come some really fundamental shifts in behaviour, along with pretty poor outcomes in everything from health to life expectancy and happiness."

A study last year by Michegan University showed that adolescents exposed to the cruelties of reality television – where nasty spats along with vicious judgements of others is the entertainment – made them even more socially agressive. Music says the casual meanness on shows like X Factor and Britain's Got Talent is an example of how cold-hearted we are becoming.

His new book, to be published at the end of the month, is called The Good Life: Wellbeing and the New Science of Altruism, Selfishness and Immorality. The latest in a series of publications to suggest a current imbalance in the UK, it collates decades of social experimental research and draws on Music's experience as a consultant to paint a grim picture of a western society undermining its natural tendency towards empathy and tipping dramatically towards nastiness.

Music disputes the notion that children are born selfish. He points to a series of experiments at the Max Planck Institute in Germany, when a group of 15-month-olds were placed in a room where an adult pretended to need help. "There is a proven urge to help. The toddlers love helping, they get an intrinsic reward just from the act, until they start to reward them for that behaviour with a toy. The group of toddlers rewarded 'extrinsically' – that is, with a toy – quickly lost interest in helping. The unrewarded children – who don't know the other group are getting rewards – keep on helping, content with no ulterior reason other than the act of helping."

Other studies have shown that toddlers feel happier giving treats than receiving them, says Music. "Then we have evidence that adolescents asked to do a good deed once a day become less depressed. We've evolved to be helpful and to do things without reward. Rewards don't make anyone happy and something very fundamental is lost when we reward for certain behaviours. We all know it, but we've lost sight of it as we're suckered into the consumer ethos, the deep insistence that we need that iPhone or that new kitchen to be happy – and we fall for it again and again. Those very powerful drivers of post-industrial capitalism and mass media are brilliant at triggering those needs and, after all, you can't sell wellbeing."

Music points to stress as keeping us in a state of "fight or flight". "It doesn't make any sense to be interested in others or what they are thinking or feeling if your nervous sytem is in flux," he said.

The book details several social experiments, including one from 1973, when theology students were told they had to give a talk about the parable of the Good Samaritan. Half were told to do it immediately; the rest were given time to prepare. As they left the room, they passed an actor who was in some trouble. Those who had to prepare quickly ignored him, while the others stopped to help.

"The speed of life has an impact on our altruism," said Music. "This is going on in schools as well. Stress is seeping into our schools with this heavily academically-based curriculum, an audit culture. I'm really worried about that from the children I see in my clinics."

Music says there is a desperate need to rethink our materialistic tendencies. "A very monetised western world is going to make us more and more lose touch with our social obligations," he said.

Maybe it's not too late to rethink that shopping trip.