We've got chemistry, baby

It's Valentine's Day again, which means I'm wondering about the same thing I wonder every year at this time: the neurobiology of love.

As far as I know there are two chemicals especially involved in love: oxytocin and vasopressin. That's not to say that they're the only two chemicals involved; dopamine and serotonin are involved in the pleasurable rewards of love, norepinephrine in the stress of love, and testosterone and estrogen in the chemistry of sex. Chemicals called pheromones might play a part in attraction, if we're anything like fruit flies. But in bonding - which, all things considered, is the hallmark of love - oxytocin and vasopressin seem to be the culprits.

Like most findings in neurochemistry, the discovery that oxytocin and vasopressin are involved in love was made through experiments with model organisms rather than humans. In studies with rats, oxytocin was found to be instrumental in bonding. Studies with voles found that vasopressin (or its receptor) was instrumental in fidelity, at least in males. Similar studies have been done in humans, although due to the squishy nature of genetic modification in humans, these studies are more correlational and less causal.

The chemistry of love is fascinating, but it raises an even bigger question: how much of our conscious thought is influenced by our brain chemistry? Certainly there is a large emotional component to love, and it's a bit easier to swallow that chemistry can affect emotions, over which we have no conscious control. But the idea that chemistry can influence things like attachment and fidelity, which are generally conscious decisions, raises an important ethical and philosophical question: if chemistry affects our thoughts, how responsible are we for our own actions?

My answer is that we are still completely responsible. Actions will always render consequences, and to pretend that because we are not in control we have not caused an effect is patently absurd. For example, if a man were to cheat on his wife and claim that his vasopressin levels made him do it, it would not undo the fact of his infidelity. I believe that, philosophically, we cannot excuse a transgression simply because of the circumstances leading up to it. As neuroscience discovers more and more about the workings of the mind, this is a stance that I believe becomes more and more valid, because ultimately nobody is completely in control.

The chemistry of love and the ethical debate about free will have two things in common: they're both still hot topics of discussion. Is love "just" chemistry? Does free will exist and, if not, can we reconcile it with traditional ethics?

What do you think?