What is love? Put your beer-goggles on!

This year for the early February blog post we wanted to continue writing on topics related to the celebration of Valentine's Day. Previously, we have written about the genetics of sexuality. This year we decided to embark on an even more daring task, and see what we could learn about the genetics of love.

Unlike the problems that ail our society or individuals, research into topics that might have more positive impacts appears to be much rarer. That includes the topic of love – so this is not exactly a subject that is replete with solid, published evidence.

To answer the question about the genetic roots behind love, we first turned to a 2015 article dedicated to the topic of the evolution behind romantic love. To start, let us repeat the authors’ definition: "romantic love in humans is a major underlying motivational force undergirding both monogamy and long-term pair-bonding". Yeah, this sounds romantic already! Well, that actually described the outcome of romantic love but why would that even exist? Likely, to increase the probability of the survival of children until they too can have their offspring (enhancing the reproductive fitness of the species). Second, the authors proposed that it might have also enhanced the evolution of human social intelligence (which probably brings us back to enhanced reproductive fitness).

To really get into what we define as romantic love, let us dive into Sternberg’s famous triangular theory of love, made up of passion, intimacy, and commitment. Passion is the sex that initially attracts partners to one another. Intimacy is the emotional and behavioral bonding between partners. And finally, commitment is the caring that keeps partners together over time. Another way to describe it is sexual desire, warmth and trust.

To successfully reach what Steinberg describes as the consummate love, you need all three elements, otherwise you are just left with one hand in your pocket fantasizing about something you do not really have. We will refer here to this kind of love also as romantic love (even though that has its own meaning in the Steinberg’s triangle).

What research indicates is that a couple's perception of their relationship with regards to each component impacts each of the components. So that's a nice bonus! Thus in theory, the more you fool around with one another, the more you invest into each other, the more you build up all necessary components to create that ever lasting love. And the greater your perception of the quality of these components of love, the greater the likelihood of you succeeding in staying with your chosen partner.

There appear to be advantages that invested romantic love provides. One of the top ones listed by the authors is that it diminishes the search for other mates. People in committed relationships appear to see their partners as more attractive than they really are, and their relationship as better than others. Yeah, that is definitely a positive feature! That is like having your beer-goggles constantly on for your loved one! And as a consequence, your eye doesn’t wander elsewhere.

In turn, married people appear to be happier and more satisfied with life, and are significantly healthier than their nonmarried counterparts. Parents divorcing/separating, on the other hand, is strongly associated with numerous negative outcomes for children, such as poorer school performance, more aggressive behaviour, more substance abuse, and greater depression. Such findings extend to the hunter and gatherer societies that have been investigated. Thus successful partnerships are associated with better health and survival for both offspring and parents, and therefore might have been evolutionarily preserved.

There are other aspects that support the idea that we have evolved for monogamous romantic relationships. The reproductive organs of men, in terms of both the design and performance, are much more typical of pair-bonded animals than those of promiscuous animals who are built to deal with intense sperm competition for successful fertilization.

So could love be genetically driven?

There seem to be strong arguments that say yes.

Evolution of love: from baby to babe

What may come as a surprise is that the components of adult romantic love are actually similar to the intense love between parents and infants. It has been proposed that the already existing design used for offspring caring might have been evolutionarily adopted for use between the mates.

There is support for the notion that romantic love and parental offspring bonding share a biological signature. One of the molecules involved in that language of love is oxytocin. Oxytocin is a peptide molecule - a peptide is built of amino acids put together and it designates a short fragment, whereas proteins are complex three-dimensional structures involved in complex cellular tasks built with many amino acids. Think of a difference between a key that opens a door versus a factory that builds cars.

Peptides, due to their simplicity, usually are a form of a message that one location in the body will use to communicate with another location. Oxytocin is exactly such a form of communication (also called a neurotransmitter) between brain cells.

Oxytocin is released during labor and upon nipple stimulation in nursing and is believed to take part in developing the maternal bond for the offspring. Now, let us also add that you are doused with oxytocin during orgasm. Oxytocin is also released by vaginocervical stimulation and nipple stimulation during sex, and it's believed that similar pathways are used to induce the same loving bonding between sexual partners that has evolved to promote maternal bonding. Thus not surprisingly, oxytocin is also released in droves during the start of a romantic relationship and that "release" is a contributing factor to establishing pair bonding.

Oxytocin has been documented to influence human relations in a positive manner in number of experimental settings, and it is believed to achieve this through activating the brain’s reward system, or dopamine release. In other words, it is like a drug, and indeed, you could take a chemical dose of oxytocin and enhance your feeling of love towards your partner.

DNA: what's love got to do with it?

Well, oxytocin binds to oxytocin receptors in your brain, and these are coded by the OXTR gene. One investigation into mutations in the DNA of the OXTR gene showed that one particular mutation (or “single nucleotide polymorphism”, abbreviated as “SNP”, which is the polite way of mentioning mutations; “variant” is another non-provoking way) in women was negatively influencing their bonding relationship with loved ones, and even caused childhood social difficulties , including autism.

As for men, the same authors showed that a specific variation in the DNA of the AVPR1A gene (another receptor for yet another neurotransmitter called vasopressin) reduced the quality of bonding with partners, also pointing to a possible genetic association with intimate relationship building. Such men were more likely to report marital crisis, while their spouses were more likely to indicate a reduced quality in the relationship. In this case, the variation in the DNA is a result of an altered amount of a DNA segment that repeats itself. These are called DNA repeating elements.

Vasopressin, is another peptide neurotransmitter. Together with oxytocin, they are the most-studied brain signaling molecules relevant to social behavior. AVPR1A gene functions appear to be complex and varied but in part they are involved in emotional processing important for the efficient analysis of reality. But our favourite has got to be the suggestion that it is also involved in enhanced music and dance performance. Now you know why males will go to extravagant lengths to deliver a humiliating dancing performance in a bid to win lasting love. It’s in our genes! Thus next time, admire it as a spectacle of evolution instead of just giggling at what a caricature of a dance is being performed in front of you!

Now, evolutionarily why would that be? Because music and performance are a presentation of cognitive and motor abilities that would be difficult to fake by unfit and sickly individuals. There is yet another receptor! This one encoded by the DRD4 gene, and linked not only to altruistic behaviour but also sexual behaviour. Who knew how intertwined these elements could be? But this one is also part of the bigger picture mentioned above - with this gene coding for the dopamine receptor. One study showed that one variant of the dopamine receptor gene was associated with sexual intercourse and desire to have children earlier in life and another with the desire not to have children or to marry. You can see how that might be influencing your romantic dynamics.

Another specific type of DNA sequence that repeats itself inside the dopamine receptor DRD4 gene, predisposes infants to attachment problems between the infant and caregiver, which predisposes them to an increased risk of psychopathology later in life.

This same mutation had also previously been associated with the personality trait of novelty seeking, which is characterized as being impulsive, excitable and exploratory in nature and just plain being fickle.

Thus it appears that maybe love really is just an internal drug to make you feel good and, as a consequence, promote your and your offspring’s well being. This is not just some metaphor . The same brain mechanisms that evolved to govern your attachment to children or to your partner also appear to be the ones that are affected by the drugs of abuse which manipulate your internal reward systems.

Is love just an addiction?

Studies indicate that significant overlap exists between love and addiction in terms of both which brain regions are used and which neurochemicals are involved, although they are independent enough that love is a specific form of addiction. As the above reference authors opined, "love is a behavioral addiction." The reward mechanism is triggered in a different manner than what drugs do, and drug addictions do not seem to be implicated in the oxytocin and vasopressin molecular processes, but love appears to be like a drug itself. How? Read on.

Tied to the molecular machinery of your internal feel good system (the reward system) is your happiness, or what scientists sensually refer to as "positive affect". While this might be independent from “feeling love”, positive emotions do not have to be tied to loving someone so we wanted to peek into this area as there are some published genetics results on this topic.

First of all, did you know that happiness is about 60% heritable? Therefore it is known that happiness has genetic component. But it's not like you get a specific gene for happiness because this is a type of trait that is referred to as complex trait and there are likely countless genetic factors that influence its outcome.

To study such complexity and to try to fish out any such contributing factors, scientists turn to genome wide association studies (GWAS). For example, in this instance, you compare a group of exceptionally happy people with a control group (in this case your typical drab; probably slightly overwhelmed; still looking for the meaning of life, populace) and see what are the average differences in their DNA. And voila! You find something that might or might not even be real (there is always the possibility that the difference was produced simply by chance because of how people were selected into each group).

By the way, many DNA tests on the market use such GWAS results that are unverified and as a consequence you can get a DNA test these days for anything under the sun. By now there is probably a DNA test that tells you what color of clothes you should be wearing or how likely you are to be romantically predisposed to someone. A heads up - just because it has been published in scientific literature does not mean it is real (including any of the references we provide, so always tread carefully when bombarded with science ). A sense of reality only emerges when science is duplicated over and over again producing similar results. There is tons of scientific information that is simply wrong, and it is a never ending averaging of observations to come to some conclusions that we hope are accurate. This is partially why progress in medicine can be so slow because medicine has to be based on very rigorous verifications before it can be applied. This should also include the science of genetic testing which is still in its infancy – so take care in what interpretations you make or better yet get a qualified genetic counsellor to help point the way.

But going back to GWAS results, these authors were able to identify one specific DNA variation on chromosome one in African-American participants that was strongly associated with positive emotions (aka happiness). The authors then showed that presence of this DNA variant resulted in greater activation of brain regions involved in emotion and reward. But wait, it gets even better! That same DNA mutation was also found to be associated with... spiritual well-being!

But wait, there is still more! That same DNA variant was found to influence the production of a specific molecule in the brain. This molecule is a micro-RNA labeled miR-181a. Wait there is still more!! But first let us talk about RNAs. If DNA is the code that contains all of the information for cellular function, RNA is a miniature fragment copy of DNA that is then used as a blueprint to produce molecular robots within our cells (actually called proteins). The DNA is not used directly for that purpose, it is more like the blueprints’ filing cabinet.

Well, that was the long standing dogma until micro-RNAs were discovered. Micro-RNAs are super tiny RNAs (hence the name) that are also encoded by DNA but they are not used as a blueprint to build anything. Instead they actually help to regulate the degree of production of molecular robots by fine tuning how DNA, other RNAs and even proteins are used. They do so by physically interacting with any of these components. They just stick their fingers everywhere. Sometimes they will enhance the production of a desired product, and sometimes they will do the opposite. This is one of the ways how the environment can influence our biology, by affecting how these micro-RNAs are used. When micro-RNAs were discovered they blew scientific minds because basically it dramatically increased the complexity of the cell regulation and it was then that scientists collectively realized how little they truly still understand cell regulation. It is like trying to show off a horse cart when suddenly a space ship lands next to you.

What is interesting about miR-181a is that past studies suggested it may be involved in reward neurocircuitry since its production in the brain is promoted by dopamine signaling induced by cocaine and amphetamine use!

Told you love is like a drug!

The conclusion stated by the authors is that this DNA variant may increase your likelihood of feeling good by affecting your ability to more positively judge the stimuli that confronts you. That is pretty handy talent to have!

Another DNA mutation that could be modulating our ability to love is in the MOR gene which codes for... an opioid receptor. Those who possess the A118G alteration (it denotes the change in amino acids that make up the protein that is produced based on the DNA blueprint) are more likely to engage in loving relationships, be more sensitive to social rejection, and are more are susceptible to developing a fearful attachment style if they previously experienced low maternal care. They are also... at increased risk of alcohol dependence! Love always comes at a price, doesn't it?

Now, this system of neurotransmitters release is controlled by additional players, and some of them we already know. It will be interesting to see how DNA variation in these additional genes might influence this chemical concept of love. We know that tampering with these genes in mice can dramatically influence their social behaviour, so it is not a far stretch to see the possibility of genetic influence in certain human behaviours that we relate to as romantic love. But much of that still has to be deciphered.

One example includes the observation that partners who are in the early stages of love experience increased blood levels of nerve growth factor. Typically nerve growth factor regulates the survival and maturation of neurons but it also appears to control the levels of vasopressin release that we discussed above. Over time, many other such genetic factors can be expected to be discovered that together could be influencing one’s propensity to love.

Smell ya later baby (a lesson in how to handle rejection)

Another genetic contribution to your love might be a surprising one. It is the idea that your choice of your partner might be dependent on their type of Major Histocompatibility Complex (MHC). MHC genes play an important role in the immune system. They code for proteins that tell our immune system which cells in our body are infected and need to be destroyed. They code for receptors that display tiny fragments of cell-invading pathogen on the surface of that cell so the immune cells that scan our body for such anomalies can recognize this bad cell and know where to jump into action. In theory, the more MHC options you have available to you, the more likely your cells will be able to present pathogen-derived information on a cell’s surface for our immune system to recognize.

Thus the idea is that partners with differing MHC types would produce more MHC diversity in their offspring which as a consequence would be more resistant to pathogens.

But how you select your partners to recognize this diversity is the aspect that is interesting. Apparently it is smell, and you can smell your preferred partner by recognizing differences in MHC composition from yourself. This means, next time you are rejected on a date, you do not have to take it personally! It has nothing to do with your face or your personality. Just incompatible MHC genes. It happens.

So should we be screening our romantic partners genetically? Believe it or not, these services already exist, although not for the predisposition to being a romantic partner, but rather for health conditions. We at Merogenomics completely advocate for the idea that partners should screen themselves, but rather prior to having children - if love can proverbially move mountains, it can certainly overcome genetics. Screening yourself prior to having children provides you with an upfront advantage of knowing if you have potential risks of producing diseases in your offspring. For you and your partner this is valuable safeguard to have when considering all your possible reproductive options based on genetic knowledge.

But should we one day seriously screen ourselves for a likelihood of romantic attachment?

Truly, even if we worked out all the genes, the idea seems silly and potentially highly discriminatory. These are complex traits that have a complicated interplay of many factors outside your genetics. Even if such test could possibly exist, (oh it will! - dubious reasons never stopped DNA tests from reaching the market) screening each other for genetic predisposition to love would probably yield you as much success as whatever else we already employ when we screen our potential love partners. In the end, it seems like such a random shot (pun intended all you dear cupids out there), and the success rate is likely to much more depend on the amount and consistency of love that is put into a person’s life.

So this Valentine’s season, we wish all of you lots of love towards your special ones, because of and despite of your genetics!

Otherwise, maybe try a MHC Cologne or perfume for a Valentines gift?

Perhaps oxytocin laced chocolates for the ladies and vasopressin laced beer for the guys, to get you in the mood for marriage?

And if you are really into risqué, Lover’s Oxytocin Clamps?

Yeah, we will let you figure that one out on your own.

Happy Valentines and happy genomes!

This article has been produced by Merogenomics Inc. and edited by Jason Chouinard, B.Sc. Reproduction and reuse of any portion of this content requires Merogenomics Inc. permission and source acknowledgment. It is your responsibility to obtain additional permissions from the third party owners that might be cited by Merogenomics Inc. Merogenomics Inc. disclaims any responsibility for any use you make of content owned by third parties without their permission.

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