Lesley Stahl’s interview with Tara Parker-Pope on www.wowowow.com considers the myriad variations on a “good marriage;” what it means for a couple to argue well; and how we might all give ourselves a break in those first years after having children, now knowing a bit more about the ways in which they affect us. We love babies. Babies don’t dilute our happiness; they expand it. Pope’s point is rather that the presence of a newborn in the lives of a couple can displace things—spoons, blocks, romance.

Parker-Pope writes the New York Times Wellness blog; her new book, "For Better: the Science of a Good Marriage," is unafraid of using scientific tools to test emotions. Her website includes quizzes (Are you Commited? How Well do You Know Your Partner? Who’s Having the Most Sex?). Here is the exchange with Stahl:

LESLEY: Now here’s a whole area that I have to say shocked me. Let’s put it in the category of the negative effect of having children on a marriage. You write quite a bit about this, and my jaw I think was open the whole time. It’s not necessarily – in fact it’s most often not good for a marriage – particularly when the baby is first born.

TARA: Yes, it’s hard to talk about because it gets a little confusing, because we love our children so much, they bring us so much joy and happiness, and it’s important to say that overall life happiness – it is not a negative when children come into your life. Overall they bring us much joy. But in the context of the married relationship, we see consistently over time a huge drop in marital happiness when children arrive. Even though this is sort of upsetting to think about, it’s actually really helpful for couples to hear this happens, because everybody who’s ever been in this situation experiences this dramatic change in their relationship and they’re a little worried. They’re like, "Oh, my gosh, are we in trouble?" No, you’re not in trouble, you’re just normal. And even though your marital happiness is dropping, it doesn’t mean you’re unhappy; it just means that your marriage is undergoing this time of stress and change. And I think the most important lesson is from the empty nest because once kids leave home they look at these couples and their happiness just shoots up. It’s actually kind of amusing how happy we get in our marriage.

This may not be the mapping of the genome, but it’s meaningful. This new, and seemingly developing, relationship between science and love will not destroy desire, or even propose to explain how it lasts (even as it suggests how it starts). The best mystery remains. But science may make us less tough on our partners and on ourselves. It may let us relax about marriage in the same way it has let us relax about flu: not much. But it may make us aware of what we can, and cannot, control. As New York’s courts concede the need for no-fault divorce, the question of what makes marriages matter—and why they might fail—is newly relevant.