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Robert Kurzban

The Evolutionary Psychology Blog

By Robert Kurzban

Robert Kurzban is an Associate Professor at the University of Pennsylvania and author of Why Everyone (Else) Is A Hypocrite. Follow him on Twitter: @rkurzban


Published 21 February, 2013

Love is on my mind because on Tuesday my lecture in class was about the evolved function of emotions, and I focused on a few in particular, including love.

To motivate the discussion, I began by trying to persuade my students that, many-splendored thing it might be, love presents something a puzzle. Consider some apparently epically poor decisions from literature. Paris might be forgiven for falling for Helen, but was his next best option so much worse that it was worth starting a war? Could Lancelot and Guinevere not put their love aside, set against their loyalties to Arthur, King and husband? And when Romeo and Juliet believed the other to be dead, was suicide preferable to searching for another, though doubtless less compelling, mate?

While the fitness consequences of such decisions seem to speak for themselves, those who have fallen in love might be inclined toward not just answering each of these with a yes, but shouting its obvious truth with ebullient, confident enthusiasm. Who among us with the least poetry in our souls has not felt the unanswerably sublime pull of another, whose virtues so ensorcel that we feel as though we might fight, kill and, yes, die that we might be together?

And so, an evolutionary puzzle. If emotions function to guide us toward adaptive behavior, not the least of which entails making good tradeoffs in decision-making, what is this thing called love, and why does it torment us so? No one seems immune, as even the rich and powerful seem ready to make sacrifices at the altar of love, as cases from Edward VIII to John Edwards illustrate. We all dance to love’s tune and obey the pull of her strings.

In class I focus on Robert Frank’s answer to this question, presented in Passions Within Reason. Briefly, Frank views love as a commitment device. Partners in budding romances want to know that their beau will not leave them. Love, Frank argues, causes people to feel irrational affection for another, in turn motivating behavior that signals these feelings and, so, commitment. If Romeo can persuade Juliet that he will not leave her even when a mate with better properties comes along, then Romeo is better off doing just that to the extent that Juliet is swayed by evidence of his steadfastness.

Critics have worried about Frank’s answer. As a commitment device, love relies on signaling, and it’s not always clear that the sorts of signals love broadcasts are honest, in the technical, not lay, sense of the term. Protestations of ardor, perhaps especially in verse, are all to the good, but nothing in poetry’s dulcet voice prevents abandonment in life’s shadowy future. When Romeo avers that his heart never lov’d till this night, why should Juliet be swayed? Flowery verse, even set to iambic pentameter, succumbs to the economist’s charge of cheapness. Is it not as easy to leave a relationship that began with literary flights on Cupid’s wings as one that did not?

For Frank, the answer is that one simply can’t, as a psychological matter, show these symptoms of love unless one is genuinely in love, making the symptoms a reliable cue to the affliction. Though I confess to being somewhat skeptical of such arguments in principle, I sympathize deeply with the intuition. Scenes in the film Shakespeare in Love, in which the Bard pens purple prose – inspir’d by fair Viola – ring true to the viewer, as if only the muse of true passion could evoke such sentiments. If love’s lines come only of love, then do the words born of love’s muse not have some power to predict?

Poetry is not, of course, the only one of love’s products. In class I also discuss Dorothy Tennov’s notion of “limerence,” the intense feelings experienced when one finds oneself irretrievably and irrevocably in love. Tennov usefully catalogs some peculiarities of limerence, not the least of which is that people experiencing it seem, more or less, incapable of attending to anything else. As Tennov renders it, the object of one’s love dominates one’s thoughts, intruding into, and interfering with, all other aspects of life, resembling a kind of addiction, as the lover craves the loved. Further, people experiencing limerence spend an inordinate amount of time dissecting their would-be lover’s words and deeds for signs that their feelings are, or are not, reciprocated. Tennov also suggests that limerence causes a certain amount of failure to engage with reality, seeing hope for the possibility of a relationship where a more dispassionate appraisal would suggest there is little, or none.

All these symptoms might persuade a potential mate of the depths of one’s feelings, but, if all of this is right, then being in love imposes some serious costs. The obsessions of love seems to radically tilt tradeoffs toward the pursuit of the target of one’s affection and away from nearly everything else. Certainly an argument can be made about the importance of pursuing a mate, but the symptoms of limerence, and the sorts of (fictional, true) examples above make it look as though love pushes us, at least on occasion, too far.

Further, some might argue that Frank’s argument suffers to the extent that it’s right. That is, suppose love does, in fact, cause someone to stay with their current mate even when a better option comes along. If love has this effect on decision making, then the benefits of signaling commitment would have to be relatively large to offset these potential costs.  Still, to the extent feelings of love genuinely foreclose alternative options in the service of signaling commitment, a potentially treacherous tradeoff is being made. The details, of course, ought to matter. How likely is a better alternative to come along? If one does, how much better is the alternative likely to be? Love’s loyalty makes the most sense in a world in which the next best option is only marginally better than the status quo. Does love look so peculiar to us in part because of the modern world’s greater vocabulary of possible lovers? In ancestral environments, if the variance were lower, then commitment might have constituted a potentially less costly tradeoff.

To end by returning to arguably the most famous love story of all time, what are we to make of the impact of the detritus of love denied, when happily ever after eludes us? That is, if love is a commitment device, when love passes out of reach, why does it persist and torment – causing both Romeo and Juliet to endure the greatest of all fitness costs –  rather than gracefully simply fading away? The agony of unrequited love, so paralyzingly horrible, seems absurdly counterproductive, in addition to, from the point of view of the unsuccessful suitor, transcendentally painful. As an adaptive matter, it would seem that the right response to doomed courtship is resuming the search; the worst response is lover’s leap, the course favored by so many. Even those who have resisted paying the ultimate price when their favored mate proves out of reach, the aftermath of rejection seems to pose enormous costs in the form of withdrawal from life’s other pursuits. The dejection of the spurned appears as painful as it is unproductive. If there is a crueler burden with which we have been saddled by evolution than the agony of a broken heart, it is hard to imagine what it might be.

  • discoveredjoys

    I suspect that to have any sensible discussion about love you have to identify and separate the cultural wrapping from the essential pair-bonding issue. For instance, what are the cultural and emotional factors in arranged marriages? What was love like in the early Middle Ages before courtly love shaped the narrative? What forms do courting take in other mammals? Does the length and effort put into courting, or the sensitivity of partners to oxytocin, vary in proportion to the amount of male and female infant care?

    When you consider the importance of pair bonding to producing the next copies of genes in humans, I can see the signalling of commitment to be one of the key factors. But I think another key factor is the negotiated exchange of sentiments, increasing over time. I’d say that the hearts and flowers stuff does not reflect an evolutionary product in itself, but it is one of the ways of producing an acceptable environment for raising children. Hallmark must hate me.

  • Lee_Kirkpatrick

    I think that any discussion of romantic love needs to start from a broader perspective on “love” more generally, from which it can be seen that the question of love is inextricably tied to the question of altruism. As Bo Diddley famously asked, “Who do you love?” The answers generally fall into three categories: your close kin (especially parents and their offspring), your romantic partner, and your closest friend(s). These are, of course, the few people in the world in whose welfare you are genuinely invested. Love functions as a kind of commitment device in all of these cases to promote an altruistic orientation toward these individuals — rather than ignoring them, or treating them merely as social-exchange partners or as competitors. The question of “why love?” reduces largely, or perhaps entirely, to the fundamental and long-standing question, “why altruism?” 

    The kinship case is of course easy from an evolutionary perspective, but the other two are harder. Tooby and Cosmides tried to solve the friendship problem in their “Banker’s Paradox” paper in a manner that is similar, in many ways, to Frank’s commitment-device solution. I have some quibbles with parts of their explanation, but I think the key involves the idea of “yoked welfare.” Romantic love, I suggest, combines elements of both: You are invested in your spouse’s welfare in part because your spouse is the other person in the world who is most heavily invested in your offspring, and in part because your spouse is (in many if not most cultures) also a close friend (to whom your own welfare is yoked in a variety of other ways beyond childrearing). 

    There are lots of specific problems to be solved with regard to how exactly these things work, and lots of good arguments we can have, but I think the starting point for addressing questions about love is the question of altruism.

    • Alex

      I think the puzzle for Rob is the “limerance” part. The fact that you have this rapid onset of valuing the other person. That is the evolutionary puzzle that needs to be explained. 

    • rkurzban

      Thanks for your comments, Lee. I don’t really know what to make of the ideas that a discussion of love needs to start with a broader perspective. As you intimate, you don’t need a commitment mechanism for close kin relationships because there’s no temptation to defect. This suggests that the mechanisms are likely to be importantly different from those surrounding romantic love. In any case, as Alex said, there are interesting questions surrounding why people deliver benefits, but it seems to me there are additional questions, such as those surrounding limerence and heartbreak.  

      • cbjones06

        …”close kin relationships…no temptation to defect”…it has been shown theoretically [quantitatively] that there are conditions when it “pays” “ego” [reproductively] to “defect” [e.g., to disperse]…it may be in “ego”‘s self-interest and, also, in her/his kin’s self-interest[s] for “ego” to “defect” [e.g., to disperse, to cheat]…as an author of one of these papers states, empirical tests of these sorts of quantitative statements will be “daunting”…

        Blog: http://vertebratesocialbehavior.blogspot.com
        Twitter: http://twitter.com/cbjones1943

    • Lee_Kirkpatrick

      I’ll respond to Rob first, and come back to “limerance” later, as I need to explain my general framework to create a context for discussing more specific issues. 

      First, let me clarify that when I said that kinship was easy, but friendship and romantic love are harder, I was referring specifically to understanding ultimate functions/causes. It is clear from inclusive fitness theory why we should be designed in a way that leads us to be invested in the welfare of, and behave altruistically toward, close kin. The other cases can’t be explained by inclusive fitness theory so directly, so there’s more work to do. Tooby and Cosmides offered an ultimate explanation for friendship in terms of the banker’s paradox, and Frank’s ultimate explanation of romantic love involves the need to at some point stop searching for mates and get down to the business of reproducing. I think there is at least some truth to both of these, but there is plenty of room for argument. In any event, the three cases clearly require at least two, and probably three, different ultimate explanations.

      At the proximal level, however, I think the three cases have much in common. In particular, I think that “love” is a proximal mechanism that is part of the programming for carrying out the (various) ultimate functions. As Frank suggests, love for a romantic partner recalibrates or deactivates other competing systems, including mate searching, and motivates caregiving and other altruistic behavior. Something similar happens in friendship that turns off competing systems related to, say, social exchange and status competition.

      And, I think love plays the same proximal role in promoting kin-based altruism, including parental caregiving. If anyone else in the world woke you up crying every night, interrupted you every five minutes all day long — not to mention peeing and pooping on you regularly — a bunch of systems in your head would respond, let’s say, unfavorably. But when your own baby does these things, it’s cute; even the poop smells good. (At least, so I’ve been told.) Just as in the other two cases, parental love is a mechanism that turns off or recalibrates all those other systems that, in the absence of it, would lead you to respond to all these behaviors very differently if someone else had done them. That is, I disagree with your (Rob’s) statement that there is no commitment problem in kinship because there is no motivation to defect: I think there are lots of reasons to defect, all the time. If you didn’t love your evil brother, you’d let him rot in jail instead of bailing him out. If you didn’t love your kid, you would probably kill him or abandon him. (Sadly, we know that this happens from time to time — which I think is often traceable to the love system either not being activated or not functioning at full speed, for whatever reason.)

      So that’s what I mean by embedding a discussion of romantic love in the context of a larger theory of love and altruism. I think of love as a proximal mechanism/system that natural selection has cleverly fashioned — you gotta admit it’s a neat trick — to solve commitment problems in three functionally distinct kinds of relationships, despite the fact that they all have different ultimate functions. Does that make sense?

    • cbjones06

      1. …definition of “signal”/”signals” needs to be specified…
      2. …if you are using “signal” as per Ethology, then, “signal” is not a trait of an individual but of a specified unit of a population [e.g., a sex, an age class, an ecotype]…why?…
      3. …because, by definition, a “signal” is a trait evolved from a “cue” via “ritualization”…
      4. …the “trait” or “signal” or “display” is generally said to be “stereotyped”…
      5. …unless i am mistaken, current Signaling Theory [in Behavioral Ecology & Evolutionary Biology] uses “signal” in the Ethological sense…

      Blog: http://vertebratesocialbehavior.blogspot.com
      Twitter: http://twitter.com/cbjones1943

  • Kate Smurthwaite

    Well first up Romeo and Juliet are fiction, the others you mention are much-corrupted legends only possibly based on any actual people. In real life people who kill their partner vastly outnumber those who kill themselves for the benefit of their partner. We can never really know whether the king who gave up his crown for love actually didn’t really fancy the job of king and used love as a handy excuse. Even subconsciously he may not have realised what was really going on. In other cases people gave up their love for a fictional deity. People can be poor decision makers.

    Love and romance are ideals that we learn as we grow up in our society. In other cultures individuals are happy to share partners. And vastly outnumbering the number of people who sail across oceans for their partner are the people who willingly marry and raise a family with someone chosen for them by their relatives on the basis of social standing, income, education, etc. Do these people not stand as evidence that love is a western idea, much like loyalty to a football team? Which is not to say its not real or we don’t feel it, but I’m also genuinely very happy when my football team wins.

    • rkurzban

      Kate, the use of fiction was to point to the sort of phenomenon I’m interested in, rather than as data but, sure, I’m happy to concede suicide driven by unrequited love is rare. Still, even if suicide is rare, it seems to me that it’s likely that the psychological pain of losing a (potential) mate is probably widespread. Whether romantic love is universal is the matter of debate in anthropological circles. Thanks for your comments.

      • cbjones06

        …maybe “the psychological pain of losing a [potential] mate” is most “widespread” among the young & relatively young; unless i am mistaken, most of the literary examples are in early-mid-age-classes…it is tempting to suggest that the “psychological pain of losing a [potential] mate” renders reproductive-age Actors vulnerable to another [potential] mate [i.e., susceptible to exploitation]…a “just so” scenario consistent w fitness “maximization”, & testable…n.b. none of this need be conscious and/or aware…

  • cbjones06

    In my brain, your blogpost triggers some associations…
    1. …unless i am mistaken, social psychologists have found that the infatuation phase [IP] of “love” lasts +, – 16 mos…it might be productive to dissect the traits associated with “love” before and after IP begins…all of the concerns you express in the post might be analyzed with such a “before”-“after” design…e.g., is suicide more like to occur pre or post IP? do the relative [survival, reproductive, other economic] costs and benefits to Actor [“lover”] differ in each phase? Do the Fitness [differential reproductive] Optima between Actor & Recipient vary before & after IP?…obviously, researcher would need to distinguish between proximate & ultimate correlates as well as demonstrate that emotional states co-vary with behaviors observed…etc, etc…
    2. …i was, also, “motivated” to think about John Hurrell Crook’s classic comment [1970 or 71]: “Social behavior is a sub-terfuge.” Is “love”, consciously, unconsciously a subterfuge designed, so to speak, by a genotype to exploit it’s phenotype?
    3. …further, one might consider whether emotions & behaviors associated with “love” constitute “best-of-a-bad-job” tactics & strategies [T&S], “bourgeois” T&S, assessment T&S, “dead end” T&S and the like…
    4. …finally, you do not mention that “love” often leads to goofy behavior…what are the [reproductive, survival, other economic] costs and benefits of responses associated with what we term “love”? Why and in what situations are individuals just plain silly over the recipient of the actor’s “loving” responses? Cui bono?
    5. …i suggest that none of the descriptions in your blogpost or in my Comment need be assumed “conscious and aware” processes…

    Blog: http://vertebratesocialbehavior.blogspot.com
    Twitter: http://twitter.com/cbjones1943

  • http://popsych.org/ Jesse Marczyk

    A few thoughts:

    Cases of Romeo and Juliet or the war fought over Helen are, no doubt, relatively rare occurrences. Though romantic love might sometimes have some negative consequences, are those negative consequences frequent and substantial enough to matter, relative to the benefits from such acts? Admittedly, I don’t know, but, for love to have evolved, it would seem the answer to that question would need to favor the benefits, at least in the abstract sense. (In much the same way that, say, all the peacocks could be better off by not growing a tail in many regards, but the costs of not having that tail are also substantial. The same might hold for love, once some kind of competition for partner selection had already begun)

    Secondly, when discussing the signal function, I think it might be wise to consider expanding the possible targets of that signal. Is it just the partner to be who is affected, or does that signal alter the behavior of your friends, family, and potential rivals as well in ways that might assist you reaching your goal? Again, I don’t have the answer, but I have creeping suspicions that the answer might be a yes

    As cbjones06 already pointed out, considerations of the contexts, both behavioral and temporal, that characterize the ebbing and flowing of love are likely to be important as well. The intensity of love is by no means a constant and, accordingly, neither are the costs and benefits that it brings. Understanding the feeling requires understanding its contextual shifts deeply, in much the same way that understanding, say, anger does.

    • Aliera

      I think Jesse’s point about the target of the “signal” is an interesting one. So maybe it really is the case that the target is the person who rejected you and you’re showing these signals as a last-ditch effort to attract or re-attract them…
      But perhaps extreme reactions to unrequited love or rejection (in the form of creative endeavors, passionate manifestos, devotion-displays) might serve as signals of one’s ability and willingness to commit to a romantic partner in general. These signals, then, are actually – and unknowingly – directed toward new potential mates who might now consider the individual attractive as a long-term mate based on the quality, costliness, and honesty of the display.
      [Pretty much Taylor Swift’s entire career, eh?]

    • http://profile.yahoo.com/NGK226MARR7UKAXBE7DBV6IF2Y Clara

      …”secondly” point is an excellent observation…see Stu West, Pen & Griffin 2002 Science…

  • TonyDeon

    Im going through a limerence “thing” now. Im glad you pointed this out I will definitely purchase Dorothy’s book. Although I cannot stay in this liminality type of space forever it is by far a beautiful place.

  • Kai

    I guess limerance is then a way to show to others after all that one’s love-commitment is real. In the EEA other potential mates would have seen ones a) prolonged longing before a relationship and b) prolonged suffering after the relationship split up (or failed to form in the first place). If ones love could be switched on and off in matters of minutes, others would not form love-relationships with you as they saw this in the past. If that is right, then this takes romance out of love, pretty much…

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