Hundreds of years ago, having a son rather than a daughter was seen as a gift. It's still the case in some communities.
A new study by economics professor Gordon Dahl at the University of California San Diego analysed US Census data and found that not only were men more likely to propose if they knew their partner was pregnant with a boy, but they were subsequently less likely to divorce if their firstborn was a boy.
A separate study at the University of Miami found that couples with a son were more likely to still be married three years after the birth of a son than a daughter. The difference was small (in the US, 64 per cent of boys aged between 11-14 lived with their biological father compared to 61 per cent of girls) but consistent, and replicated in the demographics of several other western countries.
Various psychological hypotheses have been put forward to account for the trend, including persistent subconscious gender bias, the perception that fathers bond better with children of the same gender, and the idea that men perceive sons as replacement friends and confidants.
Recent research by Rutgers University has found that in times of financial stress, parents appear to prefer daughters - or at least are more generous to them financially - but this appears to be motivated by a desire for grandchildren.