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?

Playgrounds in hip neighbourhoods may be full of sprogs with unisex names like Sage and Riley, and big-box retailers may be ditching gendered toys and clothing, but changes in public behaviour haven’t necessarily changed private attitudes. This can perhaps be seen most clearly in parents’ communications with Google – those quiet, furtive moments, when the site’s autocomplete feature absolves even the most neurotic questions (misery may love company, but anxiety needs it). A recent analy­sis of anonymous search data found that Americans ask “Is my son gifted?” more than twice as often as “Is my daughter gifted?”, even though young girls are more likely than boys to be enrolled in gifted programmes in school. Parents also ask “Is my daughter overweight?” nearly twice as often as “Is my son overweight?”, even though boys are more likely to be fat.

People will also reveal to pollsters preferences they might keep from their families. In every Gallup poll since the 1940s, when asked which sex they would prefer if they could have only one child, Americans have consistently pulled for boys. Results from the most recent poll, in 2011, were startlingly similar to those from the first: Americans said they favour boys over girls by a margin of 12 percentage points. This preference is driven mainly by men; women are largely agnostic. “Most people will say in public that they are happy to have a boy or a girl, they just want a healthy child,” says Vienna Pharaon, a marriage and family therapist in Manhattan. “But in the therapy room, where people are more comfortable feeling vulnerable, there’s an overwhelming sense that men really do want to have a boy.”

Part of the appeal of having a child of the same sex as oneself is what Pharaon calls the “mini-me phenomenon”: parents hope to create someone who is both similar to and better than themselves. By granting their children opportunities that they themselves lacked, and by behaving as the parents they always wanted, many seek to remove the same obstacles they believe were set on their own paths as they were growing up. “A lot of parents will see themselves through their child. They think, ‘Here is where I can get it right’,” Pharaon says.

This desire is hardly exclusive to men. Faith, a woman in her mid-60s with long dark hair, concedes that it was “kind of a relief” to have daughters. “There’s something we have in common,” she says of her three girls, now women in their 30s. “At each stage of their lives I would relate to how I felt at that age, and what I wished my mom said to me.”

But among fathers, this preference is plainly more profound. Sean Grover, a family psychotherapist in New York and author of the book “When Kids Call the Shots”, suggests that this is because men often feel less intuitive as parents than women do. Mothers offer babies their first opportunity for attachment; their bodies are literally essential for nourishment. Many fathers find it takes longer to connect with their children, not only because they lack that physical bond, but also because they are often stuck at work during the day. “A lot of men complain that when the baby arrives they don’t know what to do with themselves,” says Grover. “Once you get past their bravado, they are really lost.” Some men, says Pharaon, “attach themselves to the idea that at least my boy will need me to throw a ball around.” They feel a sense of purpose in the job of modelling what it means to be a man.

Fathers also like to see themselves as “the fun dad who takes their kids places,” says Grover. Mothers often get stuck with the lion’s share of routine child care – all the cleaning and feeding and whatnot – whereas fathers tend to swoop in for more recreational experiences. So it makes sense that the activities they are most eager to share are the ones they enjoy themselves. Nick, a journalist in his early 50s with two sons, aged 22 and 14, adds that men in general tend to like “bonding over a third object”, such as technology or sports, which can seem easier to do with a boy. “Men are much more gendered in their behaviour, and in their expectations of the behaviour of their kids, than women are,” says Michael Lamb, a professor of psychology at the University of Cambridge whose research investigates parent-child relationships. “Fathers tend to be more involved and engaged with sons than with daughters, and this distinction only gets more marked over time.”

Daniel, a divorced dad in his late 30s with salt-and-pepper hair, has a great relationship with his eight-year-old daughter, whom he looks after for half the week. Over a dinner of lentils and broccoli at his flat in Brooklyn, they are quick to make each other laugh. “Daddy, stop it,” his daughter squeals as he goofily widens his big round eyes, a feature they share. “It’s fascinating,” he says later of having a daughter. “I had no idea what it was like to be a little girl. We are both kind of edu­cating each other.” He admits, however, that it has been a little hard not to be able to share his love of baseball with his child. “When I was growing up, going to a ballgame with my father was a really important experience. It was the closest thing that I saw to a religious feeling in him,” he says. “I’ve taken my daughter to ballgames, but she doesn’t really know the difference between basketball and baseball. If she was a boy, I have this feeling that it would’ve been easier to interest her in those things. It would be something that we could have in common. But I’ve done my best to let it go.”

Some men are quick to say having a daughter is a relief. Evan, a thin, bespectacled film-maker in his 30s, admits he was nervous about the prospect of “constantly proving my masculinity around a boy. I throw terribly. I would worry that if we played catch in Central Park, he’d discover his father had no arm.” He beams when he talks about his toddler daughter: “She really is the girl I always hoped I would have.”

But in my conversations with fathers, I found the attitude of Adam, a jocular businessman in his mid-30s from Durham, North Carolina, commoner. “I generally think that most adult guys have very few real friendships. We’ll go grab a beer with someone, we’ll play golf or tennis with someone, but we just don’t open up a lot in particularly meaningful ways,” he says. The hope, he explains, is that his son will ultimately fill that gap. “The possibility of shaping his preferences to match mine is attractive. It’s why we play sports together, why we read together. I’m already envisioning trying to get him to read the newspaper over breakfast. I think that there’s a very significant desire for friendship that’s heightened for fathers with sons given how few other outlets we have to create friendships.”

No one comes into my office and says ‘I have a girl and I’m disappointed and it is affecting my marriage’,” says Vicki Botnick, a marriage and family therapist in southern California. But the burden of parenting often creates tension among couples. So the fact that men with sons are often “more involved and proactive” can have a big effect on how mothers feel. After a moment, Botnick adds, “I have two daughters. When I asked my husband if he thinks this made a difference in how much he helped out, he said, ‘Yeah, I probably would feel more of a sense of responsibility if we had a son.’ It actually hadn’t even occurred to me before.”

Mothers usually lavish the same amount of time on their sons and daughters, at least when they are younger, whereas “fathers devote more to sons from the get-go,” says Lundberg. A new study of California’s paid-leave benefit, for example, found that fathers were twice as likely to take paternity leave for a son than a daughter. American time-diary data from 2003 to 2006 found that married fathers with a child between six and 12 years old spent nearly 40 more minutes per day with sons than with daughters, mostly doing things like playing sports and watching television. In married families with two children of the same sex, fathers with sons spent between 22 and 27 minutes more per day on child care, and said they had less leisure time than those with daughters. Married mothers, on the other hand, spent only around six minutes more per day with a daughter than a son.

Sons also seem to push fathers to be more productive. Studies of Americans and Germans born after 1950 found that having a child of either sex spurred fathers to bring home more bacon, but the difference between a son and a daughter was considerable: nearly 110 hours a year for Germans and around 70 hours for Americans. Lundberg, who has spent years trying to untangle the economics of child gender and parental behaviour, suggests this gap was a sign that fathers were keener to provide for families with sons. Parents of sons seem not just to earn more but also to spend more. An analysis of American consumer expenditure data from the 1990s found that married couples with one son aged 18 or younger spent 4-7% more on housing than those with a daughter, and consumed more of everything from plane tickets to meals in restaurants. Intriguingly, families with sons also spent more on “women’s goods” such as jewellery and personal services (eg, manicures and hair salons), indicating that mothers benefit when there is a boy around.

Whether or not husbands are unconsciously rewarding their wives for producing the sons they yearned for, many women are conscious of their husbands’ sizeable role in raising those boys. “My husband feels it’s his job to do the man things. He is trying to show them how a man behaves, what a man does,” says Amanda, a social worker in her mid-30s with two young boys in leafy Newton, Massachusetts. “He’ll say things that seem old school, like ‘toughen up’ or ‘shake it off’, but I think he just wants to help his little men. He is creating his own traditions of what he does as a dad. And my oldest son always likes to do things the way his dad does it.”

This extra help has a measurable impact on the quality of a marriage. When Giuliano delved into the reasons why more couples with a son stayed together after three years than those with a daughter, she found that fathers of boys were not only more likely to say they were excited to become a parent, but also more helpful around the home. Mothers of boys, in turn, were more likely to praise their husbands as fathers, and were happier in their relationships than those with only girls.

But there was a telling detail in the data Giuliano examined: the marriages in which sons made a real difference were those in which mothers were initially half-hearted about their husbands. In these “marginal” marriages, in which a mother who had just given birth said she felt indifferent towards the baby’s father, Giuliano found that sons reduced divorce rates by over 20 percentage points. Boys glued these couples together partly because fathers appeared to be more co-operative and attentive at home, but also because many of these mothers agreed with the statement that “parents should stay together, even if they do not get along.” A major reason why many women with sons stayed with their husbands was, it seems, concern for the welfare of their children.

This makes sense. A wealth of research shows that family structure – and the presence of fathers especially – makes a far bigger difference to the lives of boys than girls. A recent analysis of American adolescents, for example, found that boys who lacked a father figure at home were more likely to engage in delinquent behaviour. This effect was largely constant regardless of income or the mother’s behaviour, and often persisted into adulthood. For daughters, however, the presence of a father did not make much of a difference.

As the number of single-parent households rises, the resilience of girls may help to explain the widening academic gender gap across much of the industrialised world. A recent study of 1m children born in Florida between 1992 and 2002 found that boys born to poorly educated, unmarried mothers in neighbourhoods with bad schools were much more likely to have cognitive and behavioural problems than girls raised under the same conditions. Not only did the boys perform worse academically, but also they were more likely to drop out and sell drugs or become violent. “The mothers I see raising boys alone really struggle and suffer. I’ve seen situations in which a marriage comes apart and the mother and daughter weather the storm, they have each other, but the son really acts up,” says Grover.

“For adolescent boys who are just beginning to feel their power, both physically and socially, it is helpful to have someone who can challenge them effectively,” says Gretta Keene, a couples and family therapist in New York. Louise, a writer in London with a 17-year-old son, observes that now that her son is in the throes of adolescence, she is all too aware of the need for a “restraining male presence” in his life. She found that her son’s respect for women declined when he turned 13 or 14 – a time when “the peer group asserts more importance than the parents,” and boys seem particularly disinclined to listen to their mothers. She is now finding it more difficult to impress upon her son the need for self-control, so she relies more on her husband and her son’s teachers to “teach the boy how to master himself, his aggression, his destructiveness, those typically male attributes.”

And while having sons may encourage wives to hang on to unsatisfactory husbands, having daughters may make it easier for them to leave. Women tend to get more of their emotional sustenance from their daughters, says Botnick, and they may also feel the need to be a strong female role model. “They say, ‘I need to get out of this relationship because I don’t want my girls to think this is what a healthy marriage looks like’.” But for a boy, keeping a male role model in the picture can often seem to be more important, so mothers may feel compelled to stick it out in otherwise frustrating marriages. “I have definitely seen women keep a man around that they would rather not have in their life because they believe their boy needs a father,” says Grover.

The job of modelling manhood for the next generation is not easy. Grover offers group therapy sessions for both mothers and fathers. The differences between the two, he says, are stark. “When I go out to the waiting room to pick up the mothers, they are all grouped together, chatting, exchanging numbers, telling stories. Even before I bring them in, they’ve already started,” Grover says. “But when I pick up the men, they are all sitting far apart, playing with their phones, rarely making eye contact. But that men’s group cried more than any group I ever ran in my life. Just cried and cried and cried. Their sense of isolation was profound.” Women, he explains, “are able to bond over their feelings”, whereas men often try to suppress them. “They get irritable or pissed off or controlling. These are symptoms.”

Many of the fathers I spoke to admit that showing vulnerability to other men can be difficult. Daniel, the divorced dad in Brooklyn, recalls that, growing up, mealtimes with his brothers were a kind of “blood sport”. Even now, he observes an “impulse to snuff out every manifestation of weakness as it’s being expressed”. So it makes some sense that many men set their sights on having a son. Raising a boy affords fathers a chance to be both strong and sensitive, to be powerful yet tender. With a son, a father may believe he has been delivered an adoring male ally in an atmosphere – the home – that often feels like the domain of women.

This profound sense of kinship comes with a similarly profound sense of responsibility. Many of the men I spoke to said they understood it was their job to guide their boys through the choppy waters of adolescence. “It’s just a responsibility assumed,” says Tom, a father in his late 50s with one teenage boy. “Sometimes my wife will say, ‘Hey look, I would like you to talk to our son about such and such’, but really it’s not something we even need to talk about.” Louise, the mother with a teenage boy in London, agrees that “the father’s influence with a boy is absolutely key.” She adds that male friends with sons have confided to her that they are more apprehensive about abandoning their families. “They worry more about the guilt and the damage they may cause.”

Mitchell, a Manhattan father in his 50s with five sons between the ages of six and 17, has little doubt that his wife would have a tough time if he was no longer in the picture. “There’s a different kind of bonding that happens with the father,” he explains. He mentions a conversation he had with his party-bound 15-year-old son the night before. “I can communicate with him about how I expect him to behave more effectively than his mother can, because it’s a guy talking to a guy. With me it sounds like good helpful advice; with my wife, it sounds more like she’s being overbearing and controlling.” Now that his boys are in their teens, he finds he is often defusing misunderstandings between them and their mother. “It’s just harder for her to know where they are coming from.”

If sons make fathers feel more useful, and leave mothers feeling more inept, it makes sense that they are more likely than daughters to glue couples together. But it bears noting that identifying more closely with a child can often come at a cost. A number of the fathers I spoke to found that their relationships with their sons were not only more intense than those with their daughters, but also more fraught. Grace Malonai, a clinical therapist in San Francisco, observes that men tend to be especially gentle with their young sons, but they grow more critical as the boys get older. “There just seems to be more expectation and disappointment if they are not behaving the way they ought to. With the girls, they may feel the disconnect, but they are not as harsh in their expectations.” Matt, the father in the bar in Brooklyn, says he finds it especially hard to see his son suffer, “because it’s a little like seeing myself suffer. It’s like I’ve been given another chance, and I haven’t succeeded in making it better for him than it was for me.”

Perhaps the problem is that it is never quite possible to “get it right” with a child. Parenting is a messy, humbling business, full of grand expectations, mundane fears and long days. Most of the people I talked to found that life and experience regularly challenged their assumptions. Sons may nudge some fathers to take on more responsibility, while daughters may make it easier for mothers to ditch disappointing husbands. But most parents see a child’s sex as simply one of the many characteristics that can make their job seem easier or harder at any given moment. Ultimately parenting is an endless game of trial and error, and no one gets to be perfect. The most any­one can hope for is that mothers and fathers do the best they can and then, when the time comes, try to get out of the way.■

Photographs Perou