Why do we marry? For Christians, why is God so keen on marriage? And even more specifically, why does God restrict sexual activity to marriage?

I'd like to start addressing these questions by first discussing the leash principle.

I believe the leash principle was first articulated by E.O. Wilson. The basic idea is this:

A. Does culture have human nature on a leash?

B. Or, does human nature have culture on a leash?

If it's A we have the notions of the blank slate and behaviorism where culture pulls human nature, shaping it as we would silly putty. But if it is B, then many of the cultural systems we see around us actually exist to accommodate the demands created by a pre-existing human nature.

For example, let's look at marriage. Is marriage a cultural innovation that shapes human nature? Or is marriage a response to human nature?

I deploy the leash principle here as it gives us interesting questions to ask as we approach topics where human nature and cultural institutions (like marriage) interface.

But let's back up and look at current religious conversations about sex and marriage.

In the Judeo-Christian tradition, sex is reserved for marriage. Oftentimes people ask, why is this so? Two responses typically follow. First, there is the answer from Divine Command: God just says so. Fine, but WHY does God link sex and marriage? What is His reasoning?

In response to this second question we typically get what I'll label the harm narrative. The harm narrative is this: If you have sex outside of marriage you'll be psychologically harmed. The harm isn't physical, but if you have sex outside of marriage something is "broken" inside you that never can be recovered and the integrity of your personhood is damaged or compromised.

Now, the reason the harm narrative gets deployed is that, for most Christians, there has to be something damaging about sex outside of marriage. Otherwise, why would God be so keen to prohibit it? In short, sex has got to be not just bad, but bad for you. That is the harm narrative.

Let's look a little more closely at the harm narrative:

First, given the role of sex in our adaptive history the harm principle seem dubious on the face of it. We are sexual creatures and modern American marriage rituals are relatively new in evolutionary history. Thus, it is a tall order to claim that sex outside of current American marriage rituals is psychologically harmful. Such a claim willfully ignores 3.5 million years of sex.

Second, the harm of sex might actually be due to the harm narrative. That is, it could be argued that the shame, guilt, loathing, and sense of brokenness related to amartial sex is a product of telling people that they SHOULD be screwed up if they have sex outside of marriage. If so, it might be the Christians who are harming people.

Third, given the data, I don't think the harm narrative is true (this follows from #1). This creates the following predicament: Non-Christians begin to suspect that Christians tell lies to get people to conform to Christian values.

So we return to the question: Why marriage? Why sex within marriage? I've just suggested that the harm narrative is not a good answer to these questions. Worse, the harm narrative might actually be causing the harm. Worse still, the harm narrative might make Christians look like liars. But if the harm narrative is shelved is there another rationale for "Why marriage?" and "Why sex within marriage?"?

Evolutionary psychology gives us one: Sexual rivalry and jealously.

Evolutionary psychology suggests that sex is like food. It is a finite resource that people compete for. The biological imperative is to reproduce ("Be fruitful and multiply!"). If so, how do you coordinate the sexual marketplace? Enter the leash principle. That is, human nature (the imperative creating a volatile sexual marketplace) creates an adaptive problem for human societies. How do we allow mating to occur without competition escalating into violence?

Because violence due to sexual rivalry is THE problem of sex. The problem isn't psychological harm; it's the possibility of social disintegration. For example, as I've blogged about before, homicidal fantasies are intimately tied up with sexual rivalry and jealously. As another data point, sexual jealously is the number one cause of domestic violence.

The point, then, is this: Marriage (and binding sex to marriage) is a cultural innovation to reduce communal violence (due to sexual rivalry and jealously).

With this notion in hand we see why the marital diversity in the bible (the OT patriarchs were polygamous) and across cultures makes sense. The goal of marital rituals is not to find God's "ideal plan" for a man and a woman. God's plan is to inhibit human violence. And there are many different kinds of ways that one might use to regulate the sexual marketplace. Take an anthropology course and you'll see what I mean. Overall, marital customs regulating the sexual marketplace are probably the greatest non-violence innovation in human history. Thus, the issue isn't HOW you regulate the marketplace but that it IS regulated in some fashion.

What I'm suggesting is that God's plan for marriage might be less about the couple and more about the entire community. Marriage is a sociological intervention, it's not a psychological intervention.

If this is correct then the theological conversation about sex should move away from the harm narrative ("Sex is bad for you") to sociological issues of envy, jealously, covetousness, "using people," harm, and communal violence. Marriage is about these issues. It's not about protecting you from sex.