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The Science of Love

Amelia's picture

“Why do we fall in love?” is a widespread question in society. From the popularity of this question, and the lack of sufficient research to answer it, our presentation topic was created. We felt that this topic involved all aspects of the NBS concentration (and what it stands for), and would lead to an interesting, informative, and thought-provoking discussion stemming from the many un-answered questions of love. The first half of our presentation offered current evidence for why, and how, people may fall in love. While there are numerous theories that attempt to answer the question of why we fall in love, evolutionary theory seems to point to a reason for such emotions as an adaptive strategy.

Natural selection is a major driving force behind evolutionary theory. In natural selection, heritable traits that are helpful for survival and reproduction become common in a species because individuals with advantageous traits are more likely to reproduce successfully, so more individuals in the next generation have these traits. Pinker, and other theorists, hypothesized that love and affiliation may have evolved in this way because they are adaptive traits (Pinker, 1997). When examining affiliation, animals that live in groups show affiliation for one another, and group living is thought of as an evolutionary adaptation since there are more animals to watch for danger or to confuse predators. Furthermore, by associating with other animals, more information can be learned vicariously about the environment though others in the social group. From these observations as to the benefits of social groups, it seems as though animals have evolved by relying on social bonds for survival, and with that, have first evolved to have emotions that bond them with other members of their society (such as love).

Pinker suggests in the TIME article that there is a particular need for the emotional bond of love between a male and female: the investment in raising children. He argues that love is simply a “deal closer” between these two people (Pinker, 2008). While many people in our discussion wanted to equate this love with monogamy, as Professor Le said, humans are in fact not monogamous by nature. Therefore, this desire for us as humans to tie love to monogamy may be based more heavily on the investment in raising children and the social implications and hardships that would entail by not having a partner to help you, than an actual link between love and monogamy. You can have love without monogamy, and monogamy without love.

One topic of discussion that led from the presentation of the possible adaptiveness of love was if researchers should even continue to study the science of love. Several reasons supporting the continuation of this research were brought up in class. Some of these are the idea that there is clear significant individual variation and that scientists from a variety of backgrounds can come together to ask questions that they would not have been able to ask within their own discipline. Collaborative research offers new perspectives for all involved, and enhances the conclusions one can make. Some people during discussion seemed resistant to furthering research on the science of love, mainly because of problems with methodology, and a questioning of what one can draw from studies of love if love is so individual. Overall, however, our discussion found that people were interesting in looking as to how and why people may be experiencing loving relationships.

Little is known about the neurobiological mechanisms underlying such social relationships, in particular romantic relationships (Lim & Young, 2006). Research by Young and colleagues has attempted to study the mechanisms of social attachment and affiliative behavior comparing monogamous voles (prairie voles) to non-monogamous voles (montane voles). We presented an article that overviewed the magnitude of work done by this research group on social attachment and biological mechanisms in an attempt to offer evidence for our question of how people may fall in love.

Two particular affiliative hormones that these researchers have focused on are oxytocin and vasopressin, which play a large role in affiliation. These two closely related neuropeptides (Bielsky & Young, 2004) are found only in mammals and are two of the most highly conserved hormones across species (Argiolas & Gessa, 1991). In general, oxytocin and vasopressin synthesis is present throughout limbic and autonomic brain regions and this distribution suggests a possible role in behavior related to survival of an animal, such as affiliation with others (in particular sexual partners).

The monogamous prairie voles were found by Young to have a higher density of oxytocin receptors in the nucleus accumbens than the non-monogamous voles (who do not show partner preference). Additionally, site-specific injections of oxytocin antagonists in female prairie voles prevent the partner preference previously seen, pointing to a direct affect of oxytocin in producing this response in females. The prairie voles also have a higher density of vasopressin receptors in the ventral pallidal area (the major output to the nucleus accumbens, both of which are tied to reward). From these results the researchers concluded that oxytocin and vasopressin may be facilitating affiliation and social attachment in the monogamous prairie voles through the reward pathways, and that oxytocin plays a role in female prairie vole attachment and vasopressin plays a role in male prairie vole attachment (Young et al., 2001).

These brain regions, the ventral pallidum and the nucleus accumbens, are involved in the mesolimbic dopamine reward system, which, as Young suggests, could mean that pair-bonding activates the same reward circuitry as naturally reinforcing stimuli (Young & Wang, 2004). Reward depends on the mesocorticolimbic dopaminergic system, which consists of dopamine neurons in the ventral tegmentum area with projections to the nucleus accumbens and other areas and projections of the nucleus accumbens to the ventral pallidum (Klitenick in Young & Wang, 2004). Dopamine’s release in this circuit has been shown to be involved in natural reward and addiction behavior. Dopamine in the nucleus accumbens has been shown to be critical in the formation of the partner preference in prairie voles (Young & Wang, 2004). While dopamine release is important in pair-bonding formation, there is a question of why pair bonds are not naturally observed in other animals that show dopamine release associated with mating. The suggestion from current research is that the answer lies in the interaction between oxytocin, vasopressin, and the dopamine reward system.

These results that tie the reward system to feelings of ‘love’ have also been replicated in human brain imaging research. Two particularly interesting studies that were presented to the class described how when viewing a picture of a romantic partner, people had significantly greater activation in brain areas which are part of the brain’s dopaminergic reward system as compared to when viewing a picture of a platonic friend (Bartels & Zeki, 2000). Some of these brain areas significantly more activated were the caudate nucleus and the ventral tegmentum, which was seen in voles to be involved in pair-bonding formation. Furthermore, studies of drug abuse have found that other areas significantly activated in this study(cingulated cortex, insula, putamen) have been tied to drug induced euphoria, which seems to suggest a close link between what we think is romantic love and a euphoric state (Fisher et al., 2005).

From this research with voles and humans demonstrating that the activation of the brain’s reward system involved in addiction are also activated during love and bonding, researchers have suggested that there is an addictive quality to love. This addictive quality was a popular point of class discussion and people debated over whether the idea of ‘falling out of love’ fit with this model. Gillian explained in her online post that when looking at the dopamine reward pathway, falling out of love mimics withdrawal symptoms of people going off of drugs (which are known to cause a decrease in dopamine activity). A person who feels as though they are never going to love again may in fact be responding to a sharp decrease in their dopamine neurotransmitter levels that were previously at a constantly high level while with their partner.

The possible evolutionary adaptiveness of love (pointed to by Pinker) and possible evolutionary adaptiveness of monogamy (as seen in the vole model) led off much discussion both in class and on the forum. Danielle pointed out that since humans are socially advanced, an emotional regulatory system may be at play in individual differences in monogamy. She also brought up that monogamy might have a historical basis, since in previous times one needed a partner for better access to resources. Jenna thought it was best to un-pair love and monogamy since you could have one without the other, while another person commented that “what is the point of marriage if not an attempt to enforce monogamy?” It seemed that in general, students were willing and ready to support the evolutionary adaptiveness of monogamy but not necessarily of love. Since, however, humans are not monogamous by nature it seems too simple to eliminate love from the equation.

Ian points to a particularly good reason for why love may in fact be evolutionarily adaptive and how it may tie to the dopamine reward system seen in the monogamous voles. If love gives positive feelings (dopamine reward), this may influence decision-making, which because of this love feeling would arrive at decisions to help those people (such as a mother helping a child’s needs). Feelings of love may allow one to quickly and non-consciously decide to assist individuals who play a role in their own survival, and the survival of their genetic lineage. It seems that the identification of another animal’s emotional state is important to survival of an animal, and points to the adaptiveness of such feelings.

The second part of our presentation attempted to bring to light some interesting new thoughts on love particular to this day in age. One of these new topics is the idea of dating sites and being matched by algorithms. One such site is eHarmony, which boasts that 90 eHarmony couples get married each day and that there are over 7 Million users. People now meet potential partners through such sites, which in the case of eHarmony match people on “29 dimensions of personality” (Tierney, 2008). The core traits that they match are emotional temperament, social style, cognitive mode, and physicality. Looking at these traits, class discussion looked at how valid is it to match people on such traits. Krosania brought up in the forum that not everyone is going to ‘love’ or find love in the same way. Since this is the case, the scales seem to be invalid. However, when one looks at the marriage data of couples from eHarmony, it seems that for individual people the algorithms do work. It is not known, however, if these relationships through eHarmony last long term.

Our discussion on eHarmony also brought thoughts of ethical standards of research, and the idea that eHarmony researchers needs to abide by these standards. As Professor Grobstein stated, if researchers study the science of love, these scientists should be required to abide by the same standards that other sciences abide by: mainly the fact that the observations and procedures need to be freely available to the public. Since eHarmony does not share the formulas for making matches, there is no way for further testing to be done to measure the validity and reliability of such tests. Without sharing their data, there can be no peer review process (which is essential to the standards of science). Without publishing, it seems as though there might be some flaw that the researchers are trying to hide. Some people disagreed, saying that eHarmony research should not be considered unscientific simply because they are not sharing their formulas. Their formulas are their product, and if they shared them, they would have no business. However, without offering their formulas for others to view, there is no way of confirming if what they are selling is valid.

A further topic of interest (within the science of love) was marriage, looking in particular at the high rate of divorce in our present society and what benefits marriage may possess. Our group presented an article that discussed both the health benefits for marriage and reasons for high divorce rates in the current society. In terms of health, this article described a study where it was found that people who never married were 58% likelier to die during an 8-year period than people who were married (Oliwenstein, 2008). The article also addressed that marriage can be stressful, but marriage can relieve stress. This difference seems to depend on the relationship between the partners. Professor Morris addressed, however, the fact that these data were simply correlational and a third variable could be creating this trend. It could simply be that people who marry may have fewer instances of mental instability or suicidal tendencies. This critique points to a greater problem in love and romance human research, in that it is mainly (if not entirely) correlational and self-report.

In terms of divorce, general knowledge says that 50% of married couples get divorced. In fact, this rate is based on a flawed calculation: the annual marriage rate per 1,000 people compared with the annual divorce rate. Researchers say that this is misleading since people who are divorcing in any given year are not the same as those who are marrying, so the statistic is useless. A preferred method is to calculate how many people who have ever married subsequently divorced. While calculated in this fashion, the divorce rate has never exceeded 41%, since many people who divorce are serial divorces (divorce more than once) (Hurley, 2005)

Interestingly, there are two periods of a marriage that are most critical for the survival of the marriage (i.e., the times most divorces happen) (Gottman & Levenson, 2000). The first is 7 years into the marriage (the 7-year ‘itch’), and the second is when the first child reaches 14 years of age. This second critical period has been tied to the lowest point of marital satisfaction in married couples. An interesting note that Professor Le brought up was that a major factoring behind people breaking up is that they are bored with their partner. It may be that co-occurrences lead to the idea of ‘love’ between the people (a misattribution of euphoria), not actually the other person. While many people voiced the opinion that this is an unsatisfactory explanation of love and does not encompass the experience of love, no one was able to provide evidence why this would not be the case. An overall theme of the discussion was that biology could simply not explain everything about love. It seems, however, that it is more of an unwillingness to want to accept any explanation for love besides “it just is”. People want to believe in love, and believe in it as a special experience, and not necessarily know the reasoning behind it.

Our final topic, which we did not get a chance to discuss, was gay relationships and if they are different from straight relationships. While the article assigned was from a gay man’s point of view, he references research showing differences in interactions in gay couples versus straight couples (Cloud, 2008). These researchers found that significant differences were found in argument style (where gay couples were nicer to their partner), but that gay couples had more trouble repairing their relationship after an argument (Gottman & Levenson, 2003). Thus, relationship tension seems to be different in these couples and may lead to different reasons for breaking up.

There are several areas of research that should be expanded in the future. First of all, work should continue with vole models to determine the exact causal mechanism of monogamy in this species. While it is scary to think of the fact that monogamy could then be enacted through genetic or pharmacological manipulations (as someone mentioned in discussion), the knowledge that it would bring to the understanding of attachment, social bonding, and the evolution of such bonds would be priceless. This research could be combined with more social psychology research examining divorce rates, cheating spouses, serial divorcers to see if these people correlate with the findings in the voles.

Another direction that research could pursue would be to determine the reasoning for the correlation between marriage and health. While I believe that the evidence found in group living may mean that this could stem from an inability to interact successfully with the environment or a lack of support if the individual is compromised, it is as of yet unclear. As suggested in discussion, there could be a third variable that is causing the correlation

A final critical direction for research on the science of love to take is to investigate the role of society and culture on feelings of love. As Natsu said in our class discussion, we express love differently depending on where we are and what language we are using. While much of the current research is trying to point to some possible biological mechanisms of love, it is important to understand the influences of external forces on internal feelings. In terms of the biopsychosocial model, all of these aspects (biology, psychology, society) would influence the feeling of love. While many people seem resistant to accept love purely in these terms and to not view it as ‘special’ or unexplainable, in the end what else are we but biopsychosocial? Love can not be more than these three aspects if we ourselves, as humans, are nothing more.


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Paul Grobstein's picture


If we're not monogamous, why would we want to be? Whether through genetic or pharmacological manipulations or otherwise? Why are those likely to be any more effective than existing mechanisms to encourage monogamy?