The major, major molecule

Imagine a couple so passionately in love that they can bake a thin-crust pizza placed it in between their bodies. They have been together for years and yet, they have stayed freshly in love — the constant and feverish clash of their desires able to mute a poet. One day, the couple was asked what their secret was and they reveal it. Looking at each other with the most ardent of yearning and gratitude, they declare the mystery of the attraction which has been forged in each other’s soul. They say in one voice: “We really have to thank our major histocompatibility complex (MHC) for our love.” 

Major what? Well folks, I think anything that points to what might be responsible for (or the lack of) passion and love IS major. It is major because if the link is definitively established, then MHC would be the conducting baton for the episodes in your life that would be the emotional equivalent of firework revelry or the shattering of your very core in various intensities. MHC is a set of genes present in most vertebrates. It is already known to play a main role in the immune system — in protecting your body from substances that could hurt you and to work with those that could improve you. It is the set of genes that recognize when something does not belong to your body as in the case of allergies or transplants. And more and more, it is being suspected that it does play a role in recognizing which potential mate would be biologically compatible with you.

The Guardian’s Science Weekly Podcast last Sept. 2 chased this set of genes to so we can wrap our minds around the fact that genes play a role in what we ordinarily think are pure affairs of the heart. Camila Ruz interviewed scientists who have been doing research over the years on the MHC. This included Dr. Leslie Knapp of the University of Cambridge, Dr. Craig Roberts and Dr. Nicholas Hole.  

In the podcast, important experiments were cited where MHC has taken on the spotlight when it comes to who gets attracted to whom among humans. One of the experiments involved women being asked to smell the shirts that have been worn by different men for several nights. It turned out that the ones whom the women found most “attractive” based on smell, were the ones whose MHCs were different from theirs. We do not do this consciously but it seems that if we are attracted to someone, we really are attracted to their MHC. Biologically, being attracted to someone with a different MHC from yours would be better for reproduction since a different set of genes would be able to correct any “errors” that may be found in your own genes that are passed on to your offspring. It follows that when you have similar MHCs, there is less likely chance for correction.

Studies on couples showed that implantation by the sperm as it meets the egg takes longer in couples with similar MHCs than in couples with dissimilar MHCs so that conception is more difficult in the former. In another study of a small population, couples with similar MHCs had longer intervals in between offspring than those with different MHCs. It would seem that these genes are the implementers of nature’s design to keep the succeeding generation constantly different to ensure that it has options to cope and survive.

But for women, before you decide to wholly surrender to the bare powers of your senses to smell your way to biological conjugal bliss, you should know about MHCs and the pill. There was an experiment that revealed that women, when they are not on the pill, are more likely to be attracted to men who have a different MHC from theirs and when they were on the pill, they were attracted to those who have similar MHCs. But there was no data as to how those differences translated into the state of affairs for the women and the men to whom they were attracted.

So does this major molecule ever retire after the stage of attraction? The podcast cited a study that looked at relationships of at least two years, to see how they fared in relation to the MHCs of the couple. And whola, those who had similar MHCs turned out to be the ones who expressed more dissatisfaction and more likely to have had affairs than those with dissimilar MHCs. This is interesting as it suggests that a biologically sound choice for a mate translates into a good relationship, at least for two years. It turns out that when it comes to genes, the more “different” yours is from your mate, the more compatible you are with each other.   

I think this MHC is some kind of cosmic joke. Here we all are, feeling that we are each waging the fiercest battles to win the love of each of our lives, independent of what mom and dad or our grandparents think. And yet, evidence in the form of MHCs seems to say that the genes we have inherited have a hand in steering the direction of the choices of our hearts. Now that you know this, on your anniversary, you might want to pause and declare to your beloved: “You are the love of my life and the inevitable choice of my MHC.” As the TV character Dr. Gregory House always says: “Genetics is a powerful force.”

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