The “American Dream” is deeply rooted in the national identity of the United States. It promises that in the Land of Opportunity, any individual can climb the economic ladder and prosper through hard work and ambition alone. And yet, young Americans today are struggling to earn more than their parents did at the same age, and upward mobility in the US actually compares unfavourably to that of other industrialised nations.

So why does the idea of the American Dream persist? A new study identifies one factor that has been overlooked: the influence of the "rags-to-riches" storylines common in reality TV.

Over the past few decades, it’s become clear that experiences before birth can influence later psychological wellbeing. A mother’s stress levels during pregnancy have emerged as a key influence, for instance. Now research has found that experiences of adversity even earlier in a mother's life can ultimately impact her baby's own sensitivity to stress.