Love is a Bridge (Burner)

The BBC reported on some work by Robin Dunbar that finds that people in romantic relationships have two fewer very close friends than people not in such relationships. The simplest – and probably the best – explanation for this is the fundamental zero-sumness of time. (By the way, the Fundamental Zero-Sumness of Time was the name of my Pink Floyd cover band.)Maintaining close relationships requires time, and a new love interest reduces the amount of time one has for non-lover relationship maintenance activities. Single people who try, often with limited success, to get their coupled friend to go out for nights on the town have first-hand experience of this phenomenon.

But if it’s a time constraint, then why do you lose two close friends instead of just one? One could imagine that romantic partners take up as much time as any other close friend.

This reminded me of an idea that I had some time ago, and even did a little work on in collaboration with Alex Shaw (now at the University of Chicago). We presented a poster on the topic back at the Human Behavior and Evolution Society annual conference back in 2009.

The idea takes some of its inspiration from Robert Frank’s classic account of love, which I’ve alluded to about a year and a half ago. (Wowsa. Has it really been that long?) Frank’s account turns on the notion of commitment. Take two potential lovers, equal in all other ways, but one cannot leave the relationship while the other one can. Because all else is equal, the committed one is a better choice; a lover who can’t leave means no risk of the loss of investment in the partner. In turn, this means that potential lovers gain an advantage by signaling that they can’t leave. If I can reliably demonstrate my inability to switch mates, then I become a better choice for you, again all else being equal.

Frank thinks that the emotion of love serves this function. For Frank, love entails irrational attachment to the individual who is loved, along with appropriate emotional expressions and behavior that conveys these feelings.

I have always worried about this answer because it seems to be susceptible to love mimics. What prevents people from signaling irrational ardor, but then leaving when another, better option presents itself?

This led to the Love as Burning Bridges idea. (I want to say up front that I don’t necessarily think that this is a good idea. Just that it’s an idea.)

Suppose that it’s true that people are better off when they have a larger, rather than smaller, group of close friends. This seems plausible from the perspective of various theories of what (human) friends are for. If, for instance, they are useful for reciprocal exchange, having more rather than fewer provides more chances for mutually beneficial transactions. If friends are used as allies, for support when conflicts arise, then, again, more is better than fewer.

Suppose further that as the size of your close friendship network gets smaller, each additional loss of a close friend is even more costly. Losing a friend when you have many isn’t a big deal; losing one when you have only one is a very big deal. All of this is in service of the argument that one way to convince a romantic partner that you aren’t likely to leave is to make the cost of leaving that much higher. One way to do this is to reduce the size of one’s close circle of friends. This puts all of one’s eggs, as in were, in one basket. A lover occupying one of six close friendship slots isn’t as costly to lose as a lover occupying one of four slots.

So, could it be that adding a lover doesn’t reduce the number of close friends one maintains simply as a side-effect of spending time with them? Could it be that part of the design of the emotion of love is to neglect one’s inner circle of friends, to convey that one’s partner is such a crucial part of one’s social circle that leaving them would be very costly?

As I intimated above, I don’t have a tremendous amount of confidence in this idea. With Alex Shaw – did I mention he’s now at the University of Chicago? – we ran a priming study. Here is part of the abstract:

… in order to get the benefits from this putative commitment device, love must be honestly signaled. If love caused individuals to spend less time with friends, this would impart a cost on the person in love and could potentially act as an honest signal of commitment. To test this idea, we assigned subjects to receive either a Love or Normal day (control) prime. Subjects also then filled out a questionnaire that asked them how likely it was that they would spend time with friends, take a nap, surf the internet, or do school work after the experiment. We found that individuals in the love prime reported being less likely to spend time with friends after the experiment than individuals in the control prime condition, but that these primes did not influence the likelihood of doing other activities.

These results do not, of course, settle the issue. Having said that, the data described by the BBC report seem interesting in this context, and the smaller number of close friends for those in romantic relationship is exactly the pattern that the Bridge Burning proposal predicts. Having said that, it’s not clear to me the best way to go about putting the Bridge Building model to the test. Maybe a reader will give this some thought, and have some ideas to share at the meeting of the Human Behavior and Evolution Society in Natal, Brazil at the end of the month…


Shaw, A., & Kurzban, R. (2009, June). Love as Burning Bridges. Poster Presented at the Human Behavior and Evolution Society Conference, Fullerton, CA.

08. July 2014 by kurzbanepblog
Categories: Blog | 2 comments

Comments (2)

  1. It seems to me that your skepticism about Frank’s hypothesis stems from the assumption that the primary function of love is a signaling function, which of course raises the issue of fakeability. But I think this signaling function of love is in some sense secondary, and that the primary function of love is (genetically) selfish. I suggest that the emotional experience of “falling in love” corresponds with a drastic (and often relatively sudden) recalibration of one’s welfare-tradeoff ratio (WTR) toward the other. I think this is pretty much the same thing that happens in new mothers when they “bond” with their newborns: One becomes deeply invested in the other’s welfare, the effects of which then ripple through the brain as other psychological systems need to be recalibrated to accommodate this new priority. One consequence is that one’s WTR toward various others must be down-regulated, because one can be deeply invested in the welfare of only so many others. Previously-close friends are potential victims of collateral damage.

    Once one “decides” that he or she wants a particular potential mate to be the mother/father of one’s child (in terms of both genetic and parenting), it becomes adaptive for one to shift resources away from finding/attracting mates to reproduction and child-rearing — much as Frank likens the process to a tenant and landlord who, once a lease is signed, are both freed from the otherwise-endless process of seeking the best apartment or best tenant.

    Of course, all this only works if the potential mate goes along with the program, and the likelihood of this happening is in part a function of one’s ability to signal one’s (very real) commitment to the other’s welfare. However, in light of the above, I don’t think it is necessary to postulate additional, specialized mechanisms designed to accomplish this signaling, because the evidence of one’s (actually) increased commitment will just fall out on the table with no special effort. If one has genuinely increased his/her WTR toward the other person, he/she will behave in ways that honestly signal this — because this investment is, in fact, “honest.” One will make all kinds of sacrifices for the other, many of which would seem crazy in any other context. Spending less time with (former?) close friends might be merely one of many downstream consequences.

  2. Completely off-topic, but I saw you on the TAM2014 Panel ( and was curious: Has anyone since then tried to give concrete examples, regarding the trope you handled well with saying “Show me the data”, when EvoPsych is accused of going beyond the data and other fossilized claims.(?)

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