Just in for Valentine's Day: Falling in love may depend more on your dopaminergic system, genetics than on your heart

Valentine’s Day spoiler alert: Your dopaminergic system and genetics may have more to do with whom you fall in love with than your emotions. In fact, researchers have postulated that romantic love in humans may not be an emotion at all, but a super-developed form of the dopaminergic reward system and/or the drive to produce healthier offspring.

In both mammals and birds, researchers have extensively studied the influence exerted by the dopaminergic reward system on both preferences and choices of mate selection. To study this influence in humans, researchers used functional magnetic resonance imaging (fMRI) of the brains of 17 people who were intensely in love. They found that neural activation specific to the object of subjects’ affection occurred in the right ventral tegmental area and right caudate nucleus. These areas are rich with dopamine, and associated with both mammalian reward and motivation.

“These and other results suggest that dopaminergic reward pathways contribute to the ‘general arousal’ component of romantic love; romantic love is primarily a motivation system, rather than an emotion; this drive is distinct from the sex drive; romantic love changes across time; and romantic love shares biobehavioral similarities with mammalian attraction,” wrote Helen Fisher, PhD, Department of Anthropology, Rutgers University, New Brunswick, NJ, and co-authors Arthur Aron and Lucy L. Brown.

They added that this attraction mechanism may have evolved in humans to allow people to focus their mating energy on specific individuals to not only conserve energy, but help in choosing a mate as well.

Other studies have shown that humans may choose their partners based on genetics. Specifically, researchers have shown that people with diverse major histocompatibility complexes (MHCs) were more likely to choose each other as mates than those who have similar MHCs. They postulated that this was likely to be a result of “an evolutionary strategy to ensure healthy reproduction.”

Researchers found that the MHC—a large, diverse genetic region on chromosome 6 in most vertebrates—can affect mate selection via preferences for particular body odors. The complex plays an important role in the immune system and in reproductive success. In many vertebrate species, female preference for mates with dissimilar MHC has been shown.

To assess the biological significance of MHC diversity, Brazilian researchers conducted a study to assess mate selection in the Brazilian population. They gathered MHC data from 90 married couples and compared with MHC data from 152 randomly generated control couples. Specifically, researchers compared the number of MHC dissimilarities between the two groups.

They found that the number of MHC dissimilarities was significantly greater in the married couples.

"If MHC genes did not influence mate selection, we would have expected to see similar results from both sets of couples. But we found that the real partners had significantly more MHC dissimilarities than we could have expected to find simply by chance," said Professor Maria de Graça Bicalho, head, Immunogenetics and Histocompatibility Laboratory, University of Parana, Brazil.

MHC dissimilarity means greater genetic differences. In a mate, more genetic variability decreases the danger of endogamy, or mating among relatives, and in turn, increases the genetic variability of the ensuing offspring, a definite advantage.

Professor Bicalho and fellow researchers noted that this MHC effect may be the result of an evolutionary strategy in humans to avoid incest and improve the efficacy of the immune system.

"Although it may be tempting to think that humans choose their partners because of their similarities, our research has shown clearly that it is differences that make for successful reproduction, and that the subconscious drive to have healthy children is important when choosing a mate," concluded Professor Bicalho.