The Science of Love

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A couple weeks ago an article in The Economist made the claim that love is just a chemical addiction. That's not quite all that it went on to say, however. While this looks bad for true romantics, the conclusions those who read the whole article will find will show something much more in favor of some thoughts I've long had and that I think Christians should be excited to see scientific support for.

Prairie voles release oxytocin and vasopressin during sex. Scientists have discovered that blocking this release leads to promiscuity among voles, but otherwise they mate for life. These hormones have something to do with their monogamy. Montane voles, on the other hand, do not release these hormones during sex and do not mate for life. When artificially stimulated with these hormones on the occasion of sex, they still do not mate for life. They don't have receptors in their brains for these hormones. Other than that difference, these voles are pretty much genetically the same. That means monogamy in higher animals is not a result of more complex brains or higher-order thought processes. It's a result of the ability to receive these hormones and only that ability. (They even did genetic manipulation on these voles to give the montane voles the gene for the receptors, and that did the trick, whereas removing it from prairie voles removed their ability to form a monogamous bond).

That's the bad news for romantics. We already know that animals in general continue to eat, drink, and have sex because it feels good. These activities produce dopamine in the brain. What people have often thought is that such animal desires can be sublimated by higher emotions like romantic love or higher thought processes like rationally belief formation (e.g. knowledge that unprotected sex can lead to disease or unwanted pregnancy). This research finds a chemical basis for at least the stuff we have called romantic love. The vasopressin and oxytocin lead to an association between sex and a particular partner. For mice this association is with the smell of the mate. There's an olfactory "image" (so to speak -- think Daredevil) of the mouse's partner, and that image is associated with intense pleasure.

Humans also release oxytocin and vasopressin during sex. A study in the UK linked higher levels of these hormones in brains of students who said they were madly in love. There are similar hormonal differences involving friendship, however, and this involved a much larger area of the brain. Also, the hormones associated with what these students were calling love was focused on the part of the brain that we already know has to do with gut intuitions and narcotics. Other strong emotions involve different parts of the brain.

A closer look shows three levels of what broadly might be called love: lust, romantic love, and long-term attachment. (In my terms, these would be lust, romantic infatuation, and love. I don't see the second kind as really love, though it's often blindly called that by younger people who have never experienced love.) Lust is a craving for sex, and lustful sex leads to a brain state similar to an opium high. Infatuation has "feelings of exhilaration, and intrusive, obsessive thoughts about the object of one's affection." This is commonly called "being in love" in high school and even in college. The brain state here doesn't resemble an opium high but is more like the more permanent brain states of someone with Obsessive-Compulsive Disorder. Finally, there's what I would say is love, a permanent attachment. The brain state here is similar to what's associated with "feelings of calm, security, social comfort and emotional union." The emphasis of the study on hormonal changes in the brain is followed by a warning not to ignore cultural and social factors, which play a big role in bringing on those changes.

What does this mean? If certainly confirms the age-old wisdom that teenage "love" is not the same thing as love. The relative independence of these three levels of hormone change explains why so many people who base their relationships on teenage puppy love will fall "out of love". What most likely has happened is that they never fully reached the third stage or at least couldn't maintain it. They have perceived their love as the presence of the obsessive-compulsive features of the second stage, and when that has disappeared they assume there's no more room for love. It also explains why so many people can experience lust for someone other than the person they've bonded with for life without it interfering with that love (at least in any noticeable enough ways to stop them). The parts of the brain and hormones involved are relatively independent.

What struck me most about this, though, was that it seems to confirm something I've long believed about sex. Even someone's first sexual encounter forms some sort of bond. It's not the case that this is biologically the type of bond that causes bonding for life, but that sort of bond is already in the process with the first sexual interaction between two people. The mental link between the relevant hormones and that person are already in place, and there seems to be a natural process to try to keep it in place. Somehow some of the other higher functions of human beings can interfere with it, in a way that prairie dogs can't do, since one sexual act creates a permanent bond between these animals. That doesn't always happen with humans, but I'm wondering whether this is scientific evidence that it should.

If so, then what's different about humans to prevent it from happening? Biologically speaking, they may not know, but that's for empirical science to discover. A Christian can certainly see whatever it is as a consequence of the fall. So the romantic may be threatened by this research, but in the end it's quite friendly to Christian views about sex and love.

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Relations from Opiniatrety on February 1, 2004 6:17 PM

Earlier in comments, I remarked that "X knows Y" is a symmetric relation. Contrary to what may or may not be implied here, "X loves Y" is not a symmetric relation. This has been known to cause trouble.... Read More


Matt Weiner springs off this discussion, pointing out that "X loves Y" is not symmetric, though "X knows Y" is (when X and Y are people, anyway). I agree, even according to the highest level of love of the three biology distinguishes. See my comment over there for why.

Thank you for the post -- this is fascinating material. But one of your suggestions at the end has me very confused:

One sexual act creates a permanent bond between these animals. That doesn't always happen with humans, but I'm wondering whether this is scientific evidence that it should.

I don't even know what this means. What kind of "should" are we talking about? Is this moral? Also, it's not obvious to me that there's ever (or that it's ever conceptually possible for there to be) scientific evidence establishing any should-conclusion. (This is roughly Hume's Law.)

I think Hume's perspective on this issue is actually pretty silly once you think about it. He intends for it to be against some sort of natural law theory, but it's against pretty much any objective moral theory, and it's amazing to me how many people who hold such theories continue to say this sort of thing against natural law theory (e.g. James Rachels makes this mistake in his best-selling intro to ethics book, and what's worse is that he says the same thing I say about it when responding to emotivism and then goes and repeats what he said was wrong when it comes to natural law theory).

The problem is that Hume says there's never a fact that can give rise to a moral truth. The only way that's true is if some version of emotivism is right. Utilitarianism has facts about what creates happiness. Social contract theories will have facts about what rational people would agree to. Ethical egoists have facts about what's in your personal self-interest. All these theories then say that those facts determine what's morally right and wrong.

As for my point, I wasn't sure how the argument would go, and that's why I said I'm wondering about this. I don't think it could be a moral 'should', since the reasons it doesn't happen aren't in anyone's control -- they have to do with neurology. What I was thinking is that someone what happens with lower animals doesn't happen with us. Why might that be? It could be that we're just more advanced and realize that some things trump these biological urges. On the other hand, it might be that other hormones or urges get in the way, and our more complex neurology actually harms what otherwise would have been the case.

Why do I call it a harm? Well, it seems as if this is a goal-oriented feature of our neurology, and something is interfering with the goal. (I'm not assuming a divine mind with a goal here. Evolutionary biologists talk this way all the time to distinguish between mechanisms that evolve because they achieve a goal that favors selection and mechanisms that produces side-effects with no evolutionary advantage.) Assuming this goal is good for us (as most people would think given our appreciation for long-term relationships of genuine love and not just infatuation or lust), then it seems fair to me to think of whatever cuts off this process as short-circuiting an otherwise good effect. I guess that's what I meant by 'should'.

Now if you add in other views that I happen to hold that you don't, then it takes on deeper meaning. If there is a divine mind behind this mechanism, then the process interfering with this natural, divinely-created mechanism may well be the sort of thing that Christians would see as a result of the fall. I wasn't assuming that for my argument, though it makes more sense of the 'should' talk for those who do believe it.

This is interesting material that brings up a lot of questions. Many reductivists would be tempted to say that romantic love is 'merely' chemicals x, y, and z operative in such-and-such a fashion. And, they may be right. But, the 'merely' here seems to be similar to someone who says that tennis is merely hitting a ball back-and-forth, or that accounting is merely doing paperwork. If token-identity is right, the reduction, or identity, is just fine, but severing the physical states from our first-person experiential states and their inferential connections just leaves us wondering what the 'merely' is supposed to amount to in serious dialectical terms. Maybe romantic love is realized by these chemical states, but what change is this realization supposed to amount to in terms of our practice. Is there any normative component here? And what could it possibly be? If we're good physicalists, of what surprise should it be that everything has a physical basis? What difference should this make to what we do?

My own inclination is to say that if someone is already a reductive materialist, this shouldn't make any difference. It would be a more specific find of what states are the realizers of love, but the reductive materialist already believes that there will be such a find.

If someone isn't a reductive materialist, I think it shouldn't seem that this is all there is to love. A correlation between brain chemistry and what we call folk psychology doesn't mean that this is the only cause, that there isn't another level of explanation that's perfectly legitimate and not reducible to the chemical level, or even that there's no non-physical stuff involved.

I think the moral issues, if they come up at all, will similarly not result from what this research says but from what someone's prior view is about whether reductive materialism is true, whether reductive materialism allows for morality, whether it's legitimate to talk about purposes in nature, and whether those purposes, if they exist, affect morality for us.

So what's the point, if this research doesn't necessitate any answer to these questions? Well, it's interesting, and it does affect the shape of how you'll answer any of those questions. That may well be how I was thinking of the moral consequences of all this.

One last thing, in regards to Hume's law, or the idea that you can't derive an ought from an is. I read in a paper before many examples where you can. Here's one:
1.Everything Eustace believes is true.
2. Eustace believes that one ought to be sincere.
So, one ought to be sincere.

On reflection sometimes the only sense we can get about how you can't derive an ought from an is is that we can't derive the 'ought' from premises which don't contain it. But, so what? With valid deduction you can't deduce anything with some term x where it doesn't occur in the premises. 'Ought' terms then are just on a par with 'cause' or any other term.

Emotivists, of course, won't allow the Eustace argument, but I'm not sure what they should say. My first thought was that they'd question 2, but it's not his belief that they're questioning. He has that belief. What they question is whether that belief has any factual content. According to emotivism, the belief isn't true or false because it's not in the business of being true or false. But even so the second premise is true, since the English sentence 'one ought to be sincere' is one he believes. I would assume that's the only truth condition for 2.

I guess they should say that 1 will always be false (if he has moral beliefs, anyway), since there are some things Eustace believes that are neither true nor false (again, assuming he's got moral beliefs, which 2 tells us he does).

Still, that view seems so implausible to me that it doesn't enter any of my own reasoning on moral matters, so I myself agree with your comments. I don't think it would convince Hume, though.

Moral Naturalism: Hume's Law doesn't rule out naturalism. I'm a utilitarian who believes (a version of) Hume's Law. But utilitarianism is a *substantive claim* -- it's a moral premise. See my new post.

Eustance: "Everything Eustace says is true" is equivalent to "A1 is true and A2 is true and ... and An is true", where A1...An are everything Eustace has ever said. If some of those things are moral, then "Everything Eustace says is true" is a moral statement.

I just wrote a post referencing this discussion, and about Hume's Law generally. You might find it interesting.

Your version of Hume's Law seems to be the same as Mark's, whose comments I already expressed my agreement with. I don't think that version of Hume's Law threatens anything I said in my more explicit version.

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