Here is the reason why having a son makes a couple more likely to stay together - than having a daughter

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.

Matt, a father in his early 40s with soulful eyes, thinning hair and a ready smile, is doing his best to explain why he has a more intense relationship with his son than he does with his daughter.

Over a mojito at a bar in Brooklyn, near the flat he shares with his wife and two children, he admits that he is not a stereotypically macho guy. Most of his friends are women, he says.

He was never much of an athlete and his marriage is a fairly egalitarian two-career juggling act. Yet there is something about his bond with his boy that feels particularly profound.

Partly, he thinks, it is because his four-year-old son is older, and therefore more interesting. As the first-born, his son is also teaching Matt how to be a parent, which provokes all sorts of potent new emotions and anxieties.

But perhaps the most compelling reason is also the simplest: “I really identify with him,” Matt says. “He just looks a lot like me, and he’s like me in certain ways. Every time I look at him I see myself when I was four years old.” Of course he adores his daughter, “but it’s just different. I don’t know how to make a little girl happy the way I fundamentally know how to make a boy happy, so I worry I’m going to somehow screw that up.”

Such candour can be uncomfortable for parents. In rich countries, where children are more like luxury goods than savvy economic investments, and where gender is simply one attribute among many, parents tend to pride themselves on their open-hearted, unconditional love for every member of their brood.

Admitting a stronger emotional connection with one child over another, one sex over the other, is taboo. Yet the presence or absence of children of either sex has a real impact on the dynamics of a family – even, it seems, on whether the family survives as a unit.

Gordon Dahl at the University of California, San Diego and Enrico Moretti at the University of California, Berkeley noticed more than a decade ago that men are more likely to marry, and stay married to, women who bore them sons rather than daughters.

In an analysis of American census data, they found that men were more inclined to propose to their partners if they discovered that a baby in utero was a boy, and they were less prone to getting a divorce if the first child was a boy rather than a girl. In the event of divorce, men with sons were more likely to get custody, and women with daughters were less likely to remarry.

To confirm this relationship between sons and marital harmony, Laura Giuliano, an economist at the University of Miami, analysed a survey of parents of children born in America between 1998 and 2000. She found that couples with a son were indeed more likely to be married three years after the birth of their child than those with a daughter.

This effect can be seen in data on households across a number of rich countries, which show that adolescent boys are more likely than girls to live with both biological parents.

The difference is small – in America, for example, 39% of 12- to 16-year-old girls live without their biological father in the house, compared with 36% of 12- to 16-year-old boys – but consistent. “I have never found a single statistic on a father’s presence in the household that didn’t have a significant gender difference,” says Shelly Lundberg, an economist who specialises in family behaviour at the University of California, Santa Barbara.

What is going on here? Do fathers simply prefer sons? Or are there other forces that bind fathers to homes with boys?