Dads matter.

As we head into Father’s Day weekend, that statement may seem like a cliché. But the tragic reality is that if people seeking to redefine marriage succeed in their efforts, it will become less likely in the future that Americans will have involved fathers. After all, the best way to ensure that a father will be involved in the life of his children is by attaching him to them and their mother in marriage.

While the law might be “evolving,” children aren’t. Every child has a father and deserves a relationship with a father. They still need fathers because, among other reasons there is no such thing as “parenting”—there is mothering, and there is fathering. While men and women are each capable of providing their children with a good upbringing, there are, on average, differences in the ways that mothers and fathers interact with their children and the functional roles that they play.

Dads play particularly important roles in the formation of children. As Rutgers University sociologist David Popenoe explains, “The burden of social science evidence supports the idea that gender-differentiated parenting is important for human development and that the contribution of fathers to childrearing is unique and irreplaceable.” Popenoe concludes:

We should disavow the notion that “mommies can make good daddies,” just as we should disavow the popular notion…that “daddies can make good mommies.”… The two sexes are different to the core, and each is necessary—culturally and biologically—for the optimal development of a human being.

Social science confirms the importance of a married mother and father for children. According to the best available sociological evidence, children fare best on virtually every examined indicator when reared by their wedded biological parents. Studies that control for other factors, including poverty and even genetics, suggest that children reared in intact homes do best on educational achievement, emotional health, familial and sexual development, and delinquency and incarceration.

While the law might be “evolving,” children aren’t. Every child deserves a relationship with a father.

A study published by the left-leaning research institution Child Trends concluded: “it is not simply the presence of two parents…but the presence of two biological parents that seems to support children’s development.” According to another study, “the advantage of marriage appears to exist primarily when the child is the biological offspring of both parents.”

President Barack Obama helpfully summarized the data in a 2008 speech:

We know the statistics—that children who grow up without a father are five times more likely to live in poverty and commit crime; nine times more likely to drop out of schools and twenty times more likely to end up in prison. They are more likely to have behavioral problems, or run away from home, or become teenage parents themselves. And the foundations of our community are weaker because of it.

Obama understands why fathers are so essential for children. He grew up without his father. When he addressed the all-male graduating class of Morehouse College last year, he emphasized the importance of fathers, saying, “I have tried to be for Michelle and my girls what my father was not for my mother and me. I want to break that cycle.”

But redefining marriage sends the opposite message: It signals that men and women are interchangeable—and that mothers and fathers are replaceable. Redefining marriage makes it more about the desires of adults than the needs—and rights—of children. Just consider Spain, which has gone so far as to not list the name of mother and father on birth certificates, but instead lists the names of progenitor A and progenitor B.

At one point in American life, virtually every child received the great gift of being raised to adulthood in the marital bond of the man and the woman—the mom and the dad—whose union gave them life. Today, that number is under 50 percent in some communities, and the consequences are tragic.

Same-sex marriage didn’t cause this, but it does nothing to help it and will only make things worse. Indeed, it will lock in the distorted view of marriage as an institution primarily concerned with adult romantic desires, a view of marriage that fueled the sexual revolution, the hook-up culture, no-fault divorce, and out-of-wedlock childbearing. Enshrining this view of marriage in law through a formal redefinition of marriage makes rebuilding the marriage culture much more difficult.

The breakdown of marriage most hurts the least well-off. A leading indicator of whether someone will know poverty or prosperity is whether, growing up, he or she knew the love and security of having a married mother and father. Marriage reduces the probability of child poverty by 80 percent.

Fathers matter, and marriage helps to connect fathers to mothers and children. This Father’s Day, let’s celebrate fathers and marriage.