The Science of Love

February 28th, 2015 Brain World, Features

Since we longingly watched that cute Australopithecus saunter past on the African savannah, love has been one of our most cherished and enduring mysteries. It’s hard to define, but we sure know when we see (or feel) it.

We’re physiologically capable of mating with any member of the opposite sex, after all, but that doesn’t mean we want to. Some sense of emotional and sexual urgency drives us towards that special someone – even animals exhibit behaviors that show they’re attracted to specific mates.

The reason love is so hard to pin down scientifically isn’t just because it takes so many different forms (between friends, parents and offspring, pets, etc) but because it’s not so much a part of the evolutionary urge as we first assume. Some romantic love – like homosexuality, or the schoolyard crush we experience long before sexual maturity – serves no reproductive purpose at all.

But following the work of behaviorists, neuroscientists and evolutionary psychologists we might be on the verge of unpacking the deepest, oldest drive known to humanity.

Love as chemistry

As with every other state of being, one of love’s origins is the balance of hormones and neurotransmitters in the brain. In Survival of the Nicest (2014, The Experiment Books), science author Stefan Klein tells us what the brain hormones vasopressin and oxytocin (collectively known as vasotocin) do.

Both are produced in the posterior pituitary gland and animal studies have shown they play a part in pair bonding and social hierarchy. Oxytocin’s one of the chemicals that contributes to the feeling of elation during orgasm, and the female brain also gets a burst of it during labor – which is thought to help the mother bond with the approaching baby.

The other ingredients of love we find in the neurological soup include dopamine, norepinephrine, testosterone, serotonin and lots more associated with reward, pleasure, attachment and their suppression (which we’ll hear more about later).

Biological anthropologist, author and love expert Helen Fisher performed a unique set of experiments when she put people who were in love (both requited and unrequited) in fMRI machines to see what the brain was doing in each case.

The results, coupled with rudimentary knowledge of how certain neurohormones affect our moods, let her put together a unique picture of the evolution of sexual attraction and love. She characterizes a love affair in phases where different chemicals affect our behavior and feelings.

Testosterone, which we associate with sexual desire and aggression, is prevalent in the lust phase, which Fisher likens to having an itch or being hungry – an almost purely physical need. When we fall in love, romantic attraction is produced in part by high dopamine and norepinephrine and low serotonin. If we have a casual lover or one night stand we don’t really care who else they’re with, but falling in love makes us sexually possessive and causes that craving to be together emotionally as well as sexually.

If all goes well and our yearnings are returned, we move into the attachment phase and vasotocin plays a part in generating calm and security. That it turn leads to the pair bond behavior evolution says we were put on Earth for – giving offspring a decent chance to carry our genes into the future.

Fisher’s findings also convinced her the drive for romantic love is as instinctive as those for food and security, and another quirk of human nature means the brain activity involved in love are the same regardless of the subject. The difference between loving your husband or wife, your dog and your car might only be a matter of degree.

All of which means that love – of any kind – might be made of the same few discrete chemical parts, merely arranged in different concentrations at different times.

Taking the magic away

If that last sentence makes you bristle, spare a thought for researchers trying to explain love logically. Science has long faced criticism for simplistic reductionism, and love is one of the few areas many of us get to enjoy a little bit of mystery and magic in an increasingly secular and brutally pragmatic world.

But before you resolve not to pay attention to any findings, keep a few things in mind. First, humans aren’t segmented flatworms or bacteria. We’re the sum of much more than instincts or hormones – from individual experience and brain plasticity to hard-wired and cultural behaviors – science might never really disentangle it all.

We also shouldn’t sandbox something even as seemingly simple as a brain chemical. We tend to equate testosterone with aggression or serotonin with depression (thanks to its prominence in depression treatments), but they’re all part of a multi-stranded web of function and purpose. For example, vasopressin’s primary purposes are to retain water in the body and constrict blood vessels. We think it plays a role in social behavior and sexual motivation only thanks to recent studies.

But here’s the kicker – knowing a bit more about how love works in the brain gives us the opportunity to ‘cheat’ our nervous system a little and have the kind of love we want. According to Helen Fisher’s work, the vasotocin levels associated with a long term partnership affect hormones that play a part in romantic love and sexual arousal, which partly explains the frustrating way romance seems to fade over the years.

The reason a new love affair (as opposed to just casual sex) is so all consuming is because the associated neuro-cocktail makes us want to spend months in bed together and floods us with feelings of reward and satisfaction. Doing something novel like going on holiday or trying a new restaurant with your long-term spouse can trigger the same chemical spikes that can prompt romantic love.

Far from smooth

But as a million rock songs and movies have shown (to say nothing of anyone who’s ever experienced in), love can be as crushing as it is transcendent. Rejection, loneliness and jealousy are all part of the neurochemical package.

When it comes to survival of the species, the reason love can be so painful might be because our body knows we’ve failed at the crucial game of passing our genes on, as least temporarily. As one anthropologist said, we’re built to reproduce, not be happy.

But inside our individual heads, it can be a case study in levels gone haywire. If we’re in love with someone who doesn’t know we’re alive or laughs in our face, the pain of rejection is partly from soaring dopamine and norepinephrine levels (once again a warning not to oversimplify their functions – many assume a huge injection of the ‘happy hormone’ of dopamine will simply make us deliriously gleeful). Such brain activity can in turn reduce mental controls that normally hold us back from the murder, suicide or violence that sometimes results from love gone wrong.

Nor do the lust/romance/attachment stages of love always happen in a neatly predisposed pattern. Romantic love can peter out without leading to attachment and as many casual lovers know, lust doesn’t have to lead to romantic love.

But the opposite is also true. Orgasm produces a spike of hormones that can promote falling in love, even if you’re only in the market for a one-night stand. A rush of vasotocin can make you feel attached to a lover you’ve known half an hour.

You can feel sexually attracted to one person and form a romantic attachment or pair bond with someone else. The line between human behavior in its most raw state and centuries of cultural conditioning is blurry at best, but neuroscience might finally give us a deeper insight than we’ve ever had into our most yearned-for prize.

Hijacking nature

Understanding how brain chemistry underscores our emotional state when we’re in love raises the specter of trying to control or affect it artificially. Some recreational drugs give the brain a similar high to the euphoria of falling in love, which explains not only the addictive nature of love and lust, but also the opportunity to abuse the brains’ natural function in pursuit of pleasure.

The problem is that the matrix of body and brain is a far more finely tuned system than we understand even today, and drugs used to co-opt it are very clumsy blunt instruments. Helen Fisher has written about over-prescription of antidepressants, for example.

Selective serotonin reuptake inhibitors (such a Prozac, Lexapro or Zoloft) raise serotonin and suppress dopamine, which is one of the actors in promoting feelings of romantic love. They also kill the sex drive, and without orgasm you can cut off feelings of attachment. Too many antidepressants, Fisher fears, will interfere with the systems that regulate lust, romantic love and attachment.

A dissenting view

According to psychologist Christopher Ryan and MD Cacilda Jethá, the idea that we have an innate tendency to form pair bonds is dead wrong. In their book Sex at Dawn (2010, Harper), the authors don’t deny the strong instinctive pull of the mating instinct, but they think the pair bond is a cultural artifact from the age of agriculture.

When land, animal products and elements of our environment became property to be traded, used and protected, Sex At Dawn claims reproductive rights became just another commodity, leading to our shameful collective history of treating women, virginity and fertility as mere chattel.

Ryan and Jethá say early humans in bands of a few hundred probably indulged in their attractions to more than one partner at once, love affairs fluidly beginning and ending between multiple partners concurrently.

Where one of the lynchpins of pair-bonding is paternity certainty (why put all that effort into shepherding another man’s genes into the future?), Ryan and Jethá consider it less important under natural conditions where creating and raising kids was a far more communal affair.

Among the convincing evidence Sex At Dawn uses to support its claim is the relaxed, jealousy-free, hypersexual lifestyle of the bonobo (to whom we’re just as closely related as the far more sexually aggressive and competitive chimpanzee).

Other than that, the authors say, the proof is in the pudding. We divorce, cheat on our spouses and can be sexually attracted and in love to more than one person at once. If the pair bonded family unit is our natural state, why is maintaining it over the long term such a struggle? Maybe we’re just not built for lifelong monogamy after all.

Sex at Dawn and the pair-bond proponents might both be a little bit right. Helen Fisher discovered that modern divorce statistics show a correlation between break-ups and the biological ‘birthing cycle’ of four years. Maybe when our young can walk and communicate adequately we’re designed to simply lose interest in marriage and move on.


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