You can’t blame gravity for falling in love.
—ALBERT EINSTEIN
THE GOD OF LOVE LIVES IN A STATE OF NEED, WROTE Plato in the Symposium, a dialogue on the various forms of love in which we get sex advice from none other than Socrates! Philosophers, and of course novelists and poets, have been writing about love for millennia for the simple reason that it is a fundamental emotion that profoundly affects our lives. But precisely because love is a universal phenomenon in our species, one may wonder about its evolutionary origins, and because it is an emotion, we can also ask what mechanisms in our brain make it possible. And those questions lead us into the still young and already controversial science of love.
How can anybody seriously entertain the thought of putting such a complex human emotion as love under the scientist’s microscope without ending up looking ridiculous, or at any rate missing the essence of what is going on? For starters, we can use smelly T-shirts. In 1995 Claus Wedekind and his collaborators at the University of Bern in Switzerland published a now-famous paper in the prestigious Proceedings of the Royal Society in which they claimed that human females display clear preferences for males who smell a certain way. The researchers followed a simple protocol: they told a number of men to wear the same T-shirt for a couple of nights; then they asked a group of women to smell the shirts and rate the odors they perceived for sexual attractiveness. This sounds like a bunch of crazy scientists run amok, but there was a logic to the experiment: Wedekind and his colleagues knew that other mammals (for instance, mice) express olfactory preferences for potential mates, and that the reason for this is that an individual’s smell is related to the genes he carries at the major histocompatibility complex (MHC)—an important molecular tool of the immune response system through which our bodies defend themselves from external attack by pathogens.
So the Swiss scientists scored both the men and women in their experiment for their MHC molecular markers and then compared the data with the women’s preferences based on the smell of the T-shirts. The results were astounding: humans behave like mice, with the females demonstrating a significantly stronger preference for males who sport MHC genes different from their own. This makes perfect sense from an evolutionary perspective, because when people with different MHC genes mate, their offspring will have more genetic variants at their own major histocompatibility complex, which in turn increases the chances of that offspring surviving an infection. (It’s like having a wider array of defense weapons at your disposal: if the enemy disables one kind, you can always deploy another one.)
This is an intriguing example of how an evolutionary prediction (parents should try to maximize genetic variation in the immune response of their offspring), already borne out in the case of animal systems (mice), turns out to predict the behavior of otherwise much more complex organisms such as ourselves. Next time you are on a date, it might be good to get close enough to your potential partner to smell him and see what sort of reaction you get. (Assuming, of course, that your main goal is to have healthy children; should your pursuits have more esoteric goals, like finding a companion who can make you happy, things become much more complicated.) One piece of cautionary advice, however: Wedekind and his colleagues found that women’s ability to discriminate among men with different types of MHC disappeared if they were on a contraceptive pill. Apparently the pill’s alteration of the woman’s hormone balance in some way interfered with her ability to pick up on subtle smells, making it impossible to express a preference related to the MHC. So the best thing to do is to go on a date without chemical distractions (not just the pill, but perfumes as well), and possibly after not having showered for a couple of days.
Of course, love cannot be reduced to a simple matter of smells and hormones (despite the fact that the MHC study does give a whole new meaning to the idea of “chemical attraction” between people), and philosophers have been discussing the idea of love and its implications for human affairs at least since Plato. The ancient Greeks distinguished at least three fundamental types of love. Eros, of course, is what we today call erotic love, which has largely to do with sexual attraction. For Socrates, eros is “incomplete” because it is characterized by constant dissatisfaction, a search for the other that can never be but temporarily fulfilled (though more on why this is and how our brain actually manages it in a few moments). Philia is the sort of love we experience when we need or want to get along with other people; for Aristotle, philia includes parents, children, and lifelong friends, but also business contacts and political alliances. The last type of love, agape, is in some sense the purest: agape is the sort of love that we feel unconditionally and that leads to self-sacrifice—for instance, sacrifice to the gods (if one believes in them), but also sacrifice for a spouse or close family member (in this sense overlapping with the idea of philia), or even for an idea or pursuit, such as love of science or of truth.
Modern philosophers continue to earnestly discuss what love is, and they have proposed four different, though perhaps partially overlapping, conceptions of love that are significantly distinct from those of the ancients: (1) love as an emotion, (2) love as a “robust concern,” (3) love as a union, and (4) love as valuing the other. Let us start with the idea of robust concern. The defining feature of this kind of love is selfless interest in the other’s well-being, for his or her sake and not because we gain anything out of it. (As you may have noticed, love as robust concern is reminiscent of the ancient Greeks’ idea of agape.) In the somewhat dry and formal words of philosopher Gabriele Taylor:
If x loves y then x wants to benefit and be with y etc., and he has these wants (or at least some of them) because he believes y has some determinate characteristics ψ in virtue of which he thinks it worthwhile to benefit and be with y. He regards satisfaction of these wants as an end and not as a means towards some other end.
All right, I promise never to quote a technical paper on the philosophy of love directly again, because this is the sort of thing that gives philosophers a bad reputation. Still, what Taylor is saying is that we don’t love the other (y) because her characteristics (
) benefit us, but because they are worth cherishing in their own right. Again, in this sense we are not far from agape, as this is the same sort of love that is supposed to be reserved to the gods because they are inherently good (and that, for instance, you would rightly deny to evil entities like demons). Although this idea of selfless love has some commonsense appeal, there also seems to be something clearly amiss. As another philosopher, Harry Frankfurt, put it (not a direct quote!), the idea is that robust love is neither a matter of feelings nor a matter of opinions, but a matter of will: we love someone in a robust fashion because she acts in accordance with a set of motives and preferences that we approve of. (Think about loving your god because he is good and acts accordingly, and that you would be bound not to love him if he started behaving in an evil manner—how you know whether your god behaves one way or another is, of course, your problem, upon which I shall say nothing further.)
A second modern philosophical view to entertain is that of love as valuing the other person. The basic idea is that love means to value someone in himself or herself, and that we do so because of an appraisal that centers on the dignity of that person. If this sounds a bit abstract and detached from the real world, well, it is. But there is an important kernel that philosophers who support the value conception of love are trying to get at: the idea that a love object (a person) cannot simply be swapped for another one with similar characteristics, because this would violate the dignity of both people. Think of the “robust concern” view just discussed: there is nothing in that view that would preclude you from having the same “concern” for (that is, loving) another object with the same characteristics as the one you are loving now. You could therefore swap gods or lovers, or even love many gods and many people at the same time, as long as they share the same set of characteristics (). Some people might be okay with this, but others feel that real love ought to be more exclusive and less subject to commodification. If you are in the latter group, then the value view of love might fit you well.
The third modern philosophical perspective is of love as a union. This is the idea that what is central to love is two independent individuals forming a third, collective union, a “we” that becomes more important than and transcends each individual “I.” Some philosophers speak of this “we” entity in a clearly metaphorical way, while others seem to give a more serious ontological (pertinent to existence) status to the ensemble, almost as if it really were a new individual in its own right. (It is not clear to me in what sense the “we” of love can be anything but metaphorical, but there it is.) As with the value view of love, the union conception tries to capture something that most people who have been or are in love can relate to: the creation of a new set of priorities as the couple as a unit becomes more important than the individuals who constitute it. But therein lies a problem as well: human beings are both social and fairly individualistic animals, and one can object that a union view of love puts too much emphasis on the couple at the expense of personal space, rights, and dignity. As we all know, it is precisely this tension between joint and individual needs that often is at the root of relationship problems in real life.
Finally, we turn to the emotional view of love. In philosophy an emotion is a combination of an evaluation of the object of the emotion and a motivational response to that object. For instance, if I’m afraid of you, that means I have evaluated you as somehow dangerous to my health, and it probably also means that I am prepared to take some action against you, either defensive or evasive. Of course, thinking of love as an emotion would hardly be surprising for the nonphilosopher, but the question for us here is: What sort of understanding of the phenomenon can be gained this way? And what potential problems arise if we conceptualize love primarily as an emotion?
One thing that philosophers get out of emotional theories of love is being allowed to distinguish loving someone from simply liking someone. If love is a distinct and deeper sort of emotion than the emotions elicited by friendship or admiration, then we begin to see why those other experiences are so clearly not like love. According to several philosophers who support an emotional view of love, what accounts for much of this difference is that we share a unique narrative history with the beloved: regardless of how he or she will change throughout life, we keep accumulating common memories of events and situations that are obviously unrepeatable with anyone else. This, according to such philosophers, also explains why we don’t commonly “trade up” at the first opportunity, why we do not switch partners as soon as we meet someone with even better characteristics (call them “+”) than the one we are currently engaged with.
The problem, of course, is that as a matter of regular sociological observation, people do trade up (or trade partners at the same level, or sometimes even trade down). And it is certainly the case that shared histories do not stop people from leaving their lovers because of a variety of both external and internal circumstances. People change over time in ways that may not be predictable when a relationship gets started, and the change may amount to a sufficient reason for the two partners to decide that the continuation of the relationship is no longer warranted. Besides, if we are thinking of shared history as a powerful glue holding people together, we need to remember that we also share narratives with other people, such as friends and colleagues, but that this does not prevent us from making new friends or changing jobs.
It seems clear that all four of the major theories of love being discussed by philosophers today have problems of one sort or another. And yet they all also pick up on something right about human relationships; perhaps a clever combination of these views is warranted to begin to achieve a philosophically satisfactory account of love. However, from a sci-phi perspective, no such account could be truly adequate unless it took into account what science has to say on the subject. And if there is anything that scientists are discovering about love these days, it’s how multifaceted and complex a biological emotion it really is.
One way to summarize the science of love would be to say that it’s (almost) all about hormones and their effect on our brains, and how this in turns translates into the behaviors we exhibit—the whole thing sprinkled with a bit of reasonable speculation about the evolutionary origins of such hormone-brain links. Helen Fisher, an anthropologist at Rutgers University, has made a career of researching and writing about love (and she has turned her eye to for-profit applications of her work by teaming up with a dating website appropriately named chemistry.com). Fisher and her colleagues think that there are three phases of love; that they are characterized by specific neural correlates (different parts of the brain are differentially activated during each phase); that they are regulated by distinct hormones acting in various combinations; and that we share this basic set of processes with many primates and other mammals—or at least that minority of mammals (about 3 percent of species) that form stable couples in order to raise their offspring.
The three phases themselves will be familiar to anyone who has fallen in love in his or her life: we start with infatuation (driven by a sexual interest), continue to romantic love, and—if things keep going along that trajectory—settle into long-term attachment. (Sometimes, of course, the cycle starts all over with another partner after some years.) What is interesting is that Fisher and others have been able to show that each phase is not just defined by externally observable, socially structured behavior but accompanied by specific changes in hormonal activity that act on particular areas of the human brain. Here is your handy-dandy guide to hormonal love for future reference:
PHASE |
HORMONAL PROFILE |
Infatuation |
High levels of androgens, particularly testosterone |
Romantic love |
High dopamine, low serotonin |
Attachment |
High oxytocin and vasopressin |
Beginning with the process of infatuation, we have to remember that although testosterone is usually associated with male prowess, it is present in both men and women and elicits similar effects in them, at least in terms of sexual drive. This phase is straightforward to explain in evolutionary terms: as Richard Dawkins once aptly put it, every single one of your ancestors, unsettling as the thought may be, had sex at least once or you wouldn’t be here. Sex drive, of course, tends to be rather broadly directed, meaning that there are many individuals whom we find sexually attractive and with whom, given acceptable social circumstances, we would have sex.
Pretty quickly, however (how quickly depends on both individual characteristics and social milieu), if the conditions are right, infatuation develops into romantic love, which was certainly not invented by the Victorians. Fisher’s own book, Why We Love: The Nature and Chemistry of Romantic Love, is peppered with literary citations aimed at showing that the phenomenon is cross-cultural and has been documented since the beginning of human written history. (My favorite is a phrase apparently typical of the natives of rural Nepal: “Naso pasyo, maya basyo,” which translates as: “The penis entered and love arrived.”) Those of us who have experienced romantic love will tell you that it is a strange phase in the human condition: one becomes literally obsessed with the object of his love, losing sleep over her, always wanting to be with her and only with her. This response, chemically speaking, isn’t surprising: dopamine, one of the two chief hormones involved, is the foundation of the so-called reward system of the brain—the very same one that gives us a chemical pat on the back when we do something satisfactory and that also uses the kind of brain receptors that are sensitive to addictive drugs like cocaine. Romantic love literally is an addiction! Moreover, serotonin, the second important hormone during this phase, stays at particularly low levels in the course of romance. Low levels of serotonin are well known to be associated with obsessive behavior, and also with the tendency to behave on impulse. Sound familiar? Well, now you know where it comes from.
Some of the most intriguing results of research on romantic love, however, come from animal systems. Just because they cannot recite Shakespeare’s sonnets doesn’t mean that prairie voles do not show the exact same obsessive-compulsive behavior toward their mate that human beings do—which is not surprising since the evolutionary aim is probably the same: to convince a partner you are sexually attracted to (see infatuation above) to share her favors with you so that your genes can happily combine and be transmitted to the next generation. Now, suppose you inject a female prairie vole with a dopamine antagonist, a chemical that selectively blocks the brain’s uptake of dopamine: the result will be her sudden loss of interest in whatever male she was involved with at the time! The experiment can also be done in reverse: injecting the female prairie vole with a dopamine agonist, a substance that facilitates dopamine uptake, will make her interested in the courtship behavior of any male who happens to be nearby when the injection takes effect. Seems like the idea of a love potion (and its antidote) is no longer just a matter for fairy tales (or science fiction horror stories).
The last phase is the calmer type of feeling that replaces the initial high-testosterone sexual drive and the subsequent dopamine-directed romantic obsession: we slip into a comfortable sense of stability and form long-term attachments. Again, evolutionarily this does not take a rocket scientist to explain: stable pair-bonding is typical of animal species for which there is a premium in both parents helping to raise the offspring. This is nowhere more true than in the case of humans, for whom the new generation takes several years to become self-reliant enough for the parents to be able to relax their involvement (and, in early human societies, begin to attend to the task of making still newer progeny). As I mentioned earlier, researchers have found that two hormones play the key role here: oxytocin and vasopressin. Again not surprisingly, they are both well known to be involved in nesting behavior in other species. What’s even more convincing is that the brain receptors for these hormones are absent or much less numerous in species, such as rhesus monkeys and white-footed mice, that are promiscuous and do not engage in long-term pair-bonding.
The standard, and somewhat reasonable, objection that most people raise to this sort of chemical-neural analysis of love and other human emotions is that it is far too simplistic: surely the love that inspired Shakespeare’s sonnets (not to mention the sage pronouncements of the natives of rural Nepal) is not just a matter of chemicals and neural firings. This is of course true, but it misses the point, which is that chemicals and neural firings have a lot more to do with many facets of human behavior than most people realize or are willing to acknowledge. For instance, the sort of research discussed here also sheds some light on what happens when things don’t exactly go as they are supposed to, at least in fairy tales (you know, “ . . . and they lived happily ever after”). Take the obvious question of why romantic love usually doesn’t last. Studies show that typically feelings of romance persist for about twelve to eighteen months, although of course in individual cases that period may be much shorter or longer. (This is neural psychology, not subnuclear physics, so things are true only in a broad statistical sense.) Fisher suggests that romantic feelings don’t last because we simply can’t keep up with the stress: romantic behavior is what biologists call “metabolically expensive,” meaning that it requires a lot of effort to seduce a female (human or not). The deed is accomplished differently by different species, of course, with bowerbirds building elaborately decorated nests (which are then discarded in favor of more functional versions once the female has consented) and human beings buying dinners, diamond rings, and houses, but the concept is the same. (The male bowerbird, incidentally, is simply extraordinary: he goes so far as collecting shiny objects and even paint to “decorate” what has been described as an elaborate bachelor pad, the sole aim of which is to beguile the female.)
Another crucial and decidedly un-fairy-tale-like aspect of human love relationships that we can make sense of by thinking about biology is the striking fact that many such relationships are not monogamous or do not last a lifetime. The statistics are pretty clear: polygyny is present in over 80 percent of human cultures. (Although historically, of course, very few males have been able to afford multiple mates at the same time; see “metabolic expenses” above.) Moreover, surveys show that a whopping 30 to 50 percent of Americans (both men and women, despite cultural myths to the contrary) engage in extramarital affairs at some point or another during their lives. Finally, not only do open societies (where people are more free to follow their choices and inclinations) tend to have high divorce rates, but these rates peak around the fourth year of marriage. Why? A biologist would point out that four years is about as long as it takes for a human child to become self-sufficient enough not to require biparental care anymore. Further, plenty of mathematical models (and empirical evidence in other species) show that there is a premium for both males and females to seek a variety of sexual partners during their lifetime, because doing so increases the chances that their offspring will win the genetic lottery. The natural state for primates like us is one of serial monogamy or limited polygyny. Of course, it does not follow that what is natural is what we ought to do. (As we saw in Chapter 1, that is a well-known logical fallacy in philosophy.) If we choose to go against strong biological instincts, however, we need to be aware of the perils and difficulties of that course of action: it will cost us quite a bit of willpower, and we will be constantly putting ourselves in the position of feeling guilty just because we are thinking (although not acting) along lines that our genes, hormones, and brains laid down as the path of least resistance millions of years ago.
A better appreciation of the chemistry of love also has more immediate, practical consequences. For instance, consider the increasing number of people who take antidepressant medications. A study by the Centers for Disease Control and Prevention (CDC) released in 2007 showed that the use of antidepressant drugs tripled in the United States between 1988 and 2000. In 2005 alone antidepressants were prescribed 118 million times, and in 2004 the total revenues for this type of drug hit the astronomical amount of $14 billion. (Comparable statistics for more recent years were not available at the time of this writing.) Many people, of course, take these drugs for good reasons, and doctors are aware of an array of side effects typical of each drug, effects that need to be weighed against the benefits in each patient’s case. But Fisher and her coauthor J. Anderson Thomson Jr., in an article published in 2006, warn of additional side effects that may be below the radar of both doctors and patients. Many antidepressant medications are so-called selective serotonin reuptake inhibitors (SSRIs), which work by blocking the brain from eliminating serotonin, leaving the chemical in circulation for longer periods of time. This is necessary because serotonin has the effect of elevating one’s mood, thus countering feelings of depression. But as we have just seen, feelings of romantic love rely on low levels of serotonin; thus, patients on antidepressant medications may experience artificial changes in the way they feel about their companions, regardless of any objective change in their external circumstances.
This is more than a mere possibility, as shown by an increasing number of case studies. A typical one, quoted by Fisher and Thomson, concerns a man who started using medication to counter bouts of depression: “As appreciative as I was to have regained my health, I found that my usual enthusiasm for life was replaced with blandness. My romantic feelings toward my wife declined drastically.” Eventually he gradually discontinued his medication (under medical supervision), and his feelings for his wife returned as if by magic. Of course, it wasn’t magic, but a rather powerful example of how the help that science gives us in coping with our problems often comes with trade-offs. It is precisely these trade-offs that biologists cannot help us with in making our decisions—which is why we still need philosophers.
We have briefly examined the three types of love described by the ancient Greeks, four modern philosophical conceptions of the same, and what neurobiology (and to a lesser extent evolutionary biology) can tell us about the subject. How are we supposed to put these apparently disparate views and pieces of information together? From a philosophical standpoint, we need to recognize that the ancient Greeks’ classification was an attempt to systematize the common types of love (using the word broadly) that characterize the human experience, while the modern philosophical discussion is usually framed in terms of what may (or may not) justify our loving an individual. The two are therefore not mutually incompatible. For instance, we can recognize that there is such a thing as a distinction between philia and agape and still ask whether either or both are best understood in terms of valuing the object of our love as an example of strong union, robust concern, or a particular type of emotion.
The philosophy is also not in contradiction with the science: more than was ever possible for the ancient Greeks, we now understand, for instance, both the neurological underpinnings and the evolutionary origins of eros. The modern philosophical theory of love as emotion can be enhanced and informed by what biologists tell us concerning the reason for the existence of human emotions in general and the emotions accompanying love in particular, as well as what they say about the mechanisms of emotion. Shakespeare famously asked (in As You Like It): “What ‘tis to Love?” Neither biology nor philosophy will ever be able to substitute for the first-person experience of feeling what it is like to be in love, but they certainly give us plenty of ideas and empirical evidence to begin to answer the Bard’s question in a broader sense—and hence to use our new knowledge to further enhance our enjoyment of a purposeful life.