"Sex makes babies!" "Society needs babies!" "Babies need moms and dads!" This is what her prominent contribution to the marriage debate boils down to, says family scholar Maggie Gallagher. But social trends like divorce and cohabitation, and campaigns for homosexual persons to have the right to marry and adopt children, make it necessary to prove what society has taken for granted.

A new book, The Meaning of Marriage: Family, State, Market, And Morals, brings together a sample of the high-quality scholarship that is coming from the marriage movement today. Ms Gallagher, President of the Institute for Marriage and Public Policy, is one of the contributors. In this interview with MercatorNet she lays out the evidence for marriage, understood as the committed union of a man and a woman, as the best place to bring up children.

MercatorNet: The institution of marriage has existed in virtually every society. What is the basis of society's interest?

Maggie Gallagher: When a man and a woman come together in sexual union they usually have children. As two evolutionary psychologists have written recently, "The marital alliance is fundamentally a reproductive alliance." So this is the most likely reason for society's interest in their union: the children who constitute the next generation that society needs. Every society must try to regulate the marital relationship so that children and society's interests are protected.

MercatorNet: We have assumed that marriage protects children best, but is their clear scientific evidence this is so?

Maggie Gallagher: In the last thirty years, thousands of studies have been done on this subject, studies in psychology, sociology, economics and medicine. In virtually every way that social scientists know how to measure, children do better, on average, when their parents get married and stay married – provided those marriages are not high conflict or violent.

By contrast, every major social pathology that can trouble a child happens more often when his or her parents are not married. The majority experience at least a year of poverty and are much more likely to experience physical and mental ill health, including depression and suicide. Boys from fatherless households are two to three times more likely to end up in jail as adults. Children whose parents have divorced or never married have lower grade point averages, are more likely to be held back a grade and to drop out of school. They are also less likely to graduate from college.

When marriages fail, ties between parents and children typically weaken too. Adult children whose parents are divorced are only half as likely to have warm, close ties to both their mothers and their fathers. In one large national survey, 65 per cent of adult children of divorce reported they were not close to their fathers, compared to 29 per cent of adults from intact marriages.

MercatorNet: What is it about marriage that makes it protective for children – is it the legal recognition and social benefits, as gay marriage advocates argue, or is it something else?

Maggie Gallagher: Marriage as a legal and social institution protects children in two ways. First, it makes it more likely that a child will be conceived in a home with a committed father. Second, it increases the likelihood that the child's parents will stay together.

Let me explain. For young men and women attracted to the opposite sex, avoiding an out of wedlock pregnancy or birth, not to mention staying chaste, requires effort. They need strong motivation, and part of that motivation comes from the institution of marriage, which signals the ideal conditions for having children. It also focuses the social energy of families and the community towards supporting the young couple in this struggle.

The long-term horizons of marriage therefore create what social scientists call "selection effects" and the effects are very large. A marriage culture asks young people with what kind of person they want to have children. And the qualities that make a good mother or father—dependable, responsible, committed -- are also the qualities that make for an enduring mate, someone you will want to stay with for the rest of your life. Add to this the greater community support for marriage and the fact that it can only be dissolved by taking legal action, and the odds of its providing a stable home for children rise further.

MercatorNet: Isn't the heterosexual ideal of family based on sex role stereotypes that enlightened societies have left behind? Why do you insist that "gender matters" in parenting?

Maggie Gallagher: It is evident that men and women tend to parent differently, and the differences are more pronounced to the extent that each parent "specialises" in the aspects of parenting they find most congenial. But parents are more than caretakers doing specific tasks. Here we have to take note of the new research that is confirming the significance of gender and the evidence that it is something hard-wired into us even before birth. As the developing child seeks to understand the meaning of his or her body, both the same-sex-as-me parent and the opposite-sex-from-me parent play vital roles.

For example, what a boy gets from experiencing the dependable love of a father is a deep personal experience of masculinity that is pro-social, pro-woman, pro-child, and not at odds with love. Without this experience he is more likely to define himself in ways that lead to aggression and crime. In the same way, a girl raised without a father arrives at adolescence without the experience of what male love feels like when it is truly protective and not driven by mainly by sexual desire. In seeking masculine love she is then vulnerable to use and abuse by young males. So parental gender is very relevant to child well-being.

And so, by the way, are our genes. Evolutionary psychology, for example, is showing that men in particular are likely to be affected by the existence or absence of a biological relationship with a child, and the data on child abuse confirm this.

MercatorNet: And yet advocates of same-sex marriage and parenting cite research showing that children raised by a homosexual couple do as well, if not better than children raised by heterosexual parents. Isn't their research as good as yours?

Maggie Gallagher: It is true that there is a body of research on gay parenting contradicting the consensus that children flourish best in the intact, married biological family. But reviews of the literature on sexual orientation and parenting show that the studies tend to be flawed in design and research method. One thorough review found there were no nationally representative samples of such families, the outcomes for children were generally limited to measuring things like sexual identity and self-esteem, and there were – not surprisingly – few long term studies.

Most of the gay parenting literature compares children in lesbian families to children in single-mother families and cannot enlighten us about family structure as such. But even within this literature we find evidence that father absence is linked with poorer outcomes for children.

MercatorNet: You've devoted an enormous amount of energy to the marriage debate. Is it going to be won by evidence, or is the mobilisation of ordinary people that we see in the marriage movement (of which you are a part) more important.

Maggie Gallagher: In the end debates are won by intellectuals and artists and saints – people who persuade by reason, people who touch emotions and people who by their behaviour move us to emulate them and adopt their ideas.

All the ideas about marriage we took for granted until about ten minutes ago are not "natural". They are the products of several thousand years of culture, including polemicists winning arguments against Roman paganism, artists telling stories of what true love means and requires, and people whose holiness inspires moral confidence.

Scientific evidence is one part, but only one part. Culture wars cannot be won by mobilisation. Political victories can be won that way and politics are important. But to answer your question, forced to choose I'd say the ideas are the most important thing in winning the marriage debate.

MercatorNet: Do you ever get tired of having to prove the obvious?

Maggie Gallagher: No, actually, I find the marriage debate quite engaging intellectually. Someone very smart once said to me that science is the art of making the obvious appear strange and curious: gee, things fall when you drop them, what does that mean?

I do sometimes get praised for my brilliant interventions in the public debate and that gives me pause: I wander around and say things like "Sex makes babies!" "Society needs babies!" "Babies need moms and dads!" Gee, I must be a genius, right?

Carolyn Moynihan is Deputy Editor of MercatorNet