Social science has shown beyond any shadow of a doubt that dads matter.

But there is a lot of controversy over what exactly dads contribute. It isn’t just that two-parent households have more income, although they do. It isn’t even just that two parents are better than one, since adding a stepfather to a family doesn’t remove all the problems of single-parent households and actually introduces some new problems. I have come to believe that the secret of what dads do is hidden in plain sight, in the open secret that men and women are different. The parent of each gender contributes something unique. The two parents complement one another, offsetting each other’s weaknesses and accentuating the other’s strengths.

My husband recently did something for our family that brought this into focus for me. We are foster parents. One of the most challenging aspects of being a foster parent is letting go of the kids when it is time for them to move on. Foster parents face the empty-nest syndrome early and often.

We had a couple of very sweet kids who had lived with us for a long time. We were very attached to them and never really thought they would go home. Their parents surprised everybody by doing every last item on their case plan. The phone call finally came that made it clear that the kids would go home one day soon.

The kids were elated. I was devastated. I tried to contain myself because they were so happy. But I was visibly a wreck.

My husband came into our bedroom, chased all the kids out and closed the door. I was sobbing. I had a dozen reasons why it was all a big mistake. The kids would be better off with us, and the parents would surely collapse at the first sign of trouble, and The System is so corrupt and awful.

He held me by the shoulders, looked straight into my eyes and said, “These are not our kids. Let them go.” I wasn’t ready to stop crying, but I knew he was right.

So they went home. Their parents really had gotten themselves together. The kids did great and are still doing great. We did our job as foster parents, and our job was finished for these particular kids.

In roughly the same period of time, we became acquainted with a couple of other foster kids, similarly situated. Although these girls had a comparable probability of successful reunification, their cases unfolded quite differently. Both girls, for different reasons, dithered over whether they wanted to go home. Because they were a little older than our kids, their vote counted. Both of them had gotten used to getting their own way, more than they were likely to get away with if they lived with their respective families. Looking beneath the surface, both had anxieties about returning home, anxieties that perhaps could have been — and should have been — addressed by a confident adult.

As I reflected on how these various cases unfolded, I had to ask myself why our kids successfully reunified, and why the other two girls had gotten so tangled up. And I mean tangled: They had so alienated their foster moms that permanent placement with them was probably no longer an option. And then it dawned on me: Both these foster moms were unmarried women.

I have a lot of respect for these particular unmarried foster moms. But I think their cases illustrated some of what dads do. And what dads do are things social scientists have a hard time measuring. While these other foster moms were being bamboozled by their kids, my kids had a father to tell them “No” once in a while. And even when I told them “No,” I had Dad in the background to back me up so I didn’t cave in to their nagging. Unmarried mothers have no other adult in the household to back them up, or to hold them accountable.

Now I ask you, which of us, my husband or I, did the most for those kids? To even ask this question is to misunderstand the nature of the family, of marriage and of parenting. I certainly did more driving in the car pool and helping with homework. This is the stuff women complain about and that social scientists measure.

But he was always there, too. He’d play catch with them, encourage them to take risks and glare at them when they misbehaved. And, yes, he would sometimes tell me to get a grip when I might have gone off the deep end. At the crucial moment, he kept me from doing something really stupid and destructive. My husband gave those kids the opportunity to reunite with their parents, an opportunity I might very well have sabotaged if left to my own devices. You’d have to be a nut to believe that the number of hours each of us spent with the kids was the most relevant fact about who contributed to their success.

We have become a nation of nuts over the question of fairness inside marriage. A married couple can be an organic whole. Working together, we can do what neither of us could do separately. If we insist that men and women are interchangeable, we will overlook our spouses’ unique contributions. If we get hung up on equality, we will be too busy keeping score to appreciate each other. We won’t be able to see just how much dads really do.

Jennifer Roback Morse is

a research fellow at

the Hoover Institution.