Love in the Time of PCR

Posted by Laura Beebe on January 30, 2020 in Animals, Behavioral Neuroscience, Emotions, ethics, genetics, Hormones, Uncategorized | Leave a comment

(Image credit: CellPress) 

Renowned geneticist George Church caused a stir last month with his idea for a brand new dating app, in which users submit their DNA for sequencing as a critical part of their profile.  Church’s app, “digiD8”, doesn’t connect tech-savvy singles who love all-things-90’s, as the name implies, but rather matches users based solely on their genetic information.  The goal of “digiD8” is to eliminate genetic disease by preventing carriers from interacting– in this manner, any children produced from a digiD8 match would have a greatly reduced risk of inheriting a given genetic disease.  Of course, there are a wide variety of diseases with a genetic component, and Church was originally vague on which specific alleles digiD8 would screen for. He eventually settled on “only a subset of the most rare diseases”, about 120. But assuming your dating preferences are more nuanced than a calculated risk-assessment of offspring viability, could genetic data give us any additional insight about partner compatibility? 

The science behind social connection

Neuroscientists and ecologists have begun to untangle complex social behaviors in animals, largely through careful genetic dissection of the contributing neurons.  From mating, to parenting, to aggression, we can begin to understand the component parts behind social interconnectedness in a given species. In vertebrates, our best approximation of human dating practices may come from the practice of “pair bonding,” or social monogamy.  When organisms are pair-bonded, they stick together – they mate, hang out together, and raise offspring together (see cute owl pic above). This doesn’t necessarily preclude mating with other organisms of the same species– mating with only one partner is termed “sexual monogamy”. Interestingly, social monogamy is tied to specific phylogenies more than others.  About 90% of bird species are socially monogamous, whereas less than 5% of mammalian species practice any kind of monogamy [2,3]. 

By studying a pair of species that exhibit different bonding behaviors, we may begin to understand the genetic substrates that cause two organisms of the same species to “stick”.  Prairie voles, a type of common North American rodent, are strictly monogamous. After mating once, prairie voles prefer to spend time exclusively with their chosen partner, and male prairie voles will refuse to mate with other females.  In contrast, montane voles, a closely related species, are non-monogamous. We can quantify the behavior of the two species with a “partner preference test”, in which we measure the amount of time a mated vole spends with its previous partner versus a new, unfamiliar stranger.  Prairie voles maximize time spent with their known partners, while montane voles prefer to spend time getting to know a new vole.

Prairie voles (male and female) engage in side-to-side contact. [4]

When we look at the brains of these two species, we can observe striking differences within their limbic systems. (In humans, the limbic system has been implicated in emotional processing  [5]).  Specifically, their brains differ in their ability to respond to two important hormones, oxytocin and vasopressin. According to their sex, prairie voles show high oxytocin or vasopressin receptor expression within key limbic brain areas (see image below).  In contrast, montane voles express neither receptor in these sites. Critically, oxytocin and vasopressin receptors are required for pair-bonding behavior in prairie voles: when either receptor activity has been blocked, previously-bonded voles no longer prefer their partners.  Additionally, receptor activity also seems to be sufficient to produce pair-bonding: artificially expressing oxytocin or vasopressin receptors in the montane vole limbic system induces monogamous behavior after mating. [4]

Differences in vasopressin receptor (top) and oxytocin receptor (bottom) binding between species. [4]

From species differences in tiny voles, we can begin to understand some of the genetic basis for how mammals in general might form partner bonds with each other.  What does this mean for humans searching for love? A recent study  [6] investigated the association of slight differences in the oxytocin receptor (OTR) gene with marital satisfaction.  The OTR gene is subject to a single nucleotide change- this means that according to your personal genetics, you will carry either an “A” or a “G” allele differing by a single nucleotide. Previous literature has uncovered a role for the OTR gene in individual response to social situations [7].  In this study, the researchers focused on OTR contribution to close, interdependent relationships (i.e. marriages).  Participants in the study (in this case, 2 groups of older, heterosexual married couples) took a survey to self-report their marital satisfaction.  Additionally, the subjects generated their own attachment security scores using a modified version of the “Experiences in Close Relationships Scale” [8]. Using statistics, the researchers found that individuals who had their own “GG” phenotype, or a partner with the “GG” phenotype, experienced greater marital satisfaction and attachment security.  

These results indicate that in at least a subset of possible adult relationships, genetics may be predictive of mutual happiness.  Does that mean we should have our partners sequenced before settling down? Or better yet (as George Church may think), should we pre-screen our partners and interact only with those who are predicted to provide us with the greatest attachment security?  (Will digiD8 add a “GG” badge to users with the golden genotype?) What are we really looking for when we swipe, anyway? 

References:

1. Harvard geneticist George Church’s DNA dating app to reduce disease decried by critics as ‘eugenics’ – The Washington Post. Available at: https://www.washingtonpost.com/nation/2019/12/13/genetics-george-church-dna-dating-app-reduce-disease-eugenics/.
2. 10 examples of monogamy in the animal kingdom. Available at: http://crosstalk.cell.com/blog/10-examples-of-monogamy-in-the-animal-kingdom.
3. Lukas, D. & Clutton-Brock, T. Cooperative breeding and monogamy in mammalian societies. Proc. R. Soc. B Biol. Sci. 279, 2151–2156 (2012).
4. Young, K. A., Gobrogge, K. L., Liu, Y. & Wang, Z. The neurobiology of pair bonding: Insights from a socially monogamous rodent. Frontiers in Neuroendocrinology 32, 53–69 (2011).
5. RajMohan, V. & Mohandas, E. The limbic system. Indian J. Psychiatry 49, 132 (2007).
6. Monin, J. K., Goktas, S. O., Kershaw, T. & DeWan, A. Associations between spouses’ oxytocin receptor gene polymorphism, attachment security, and marital satisfaction. PLoS One 14, e0213083 (2019).
7. Rodrigues SM, Saslow LR, Garcia N, John OP, Keltner D. Oxytocin receptor genetic variation relates to empathy and stress reactivity in humans. Proc Natl Acad Sci U S A.ubMed Central PMCID: PMCPMC2795557. 2009;106(50):21437–41. Epub 2009/11/26. pmid:19934046
8. Brennan KA, Clark CL, Shaver PR. Self-report measurement of adult attachment: An integrative overview. Attachment theory and close relationships. 1998:46–76.