Is your perfume stopping you from finding your mate?

What an absurd question, but yes, the conclusion can be it.

What I am going to discuss next is probably the most miraculous thing you will read today. You will be amazed to learn the lengths evolutionary forces go to make the existence of a species possible. Let us begin!

We often hear “opposites attract”, for example- magnets, charges, people etc. And yes, before you start rebelling “people” as an example, I would like to say that I am not qualified to comment on the behavioral aspect [1]. I mentioned people as an example because the aspect I am going to discuss aptly presents how and why nature wants opposites to attract. I am talking about the immune system.

Our immune system is one of the largest and most widespread organ systems throughout the body, and probably the most underrated and the least understood (after the nervous system and the brain). It is too intricate to give a short description whilst also being accurate. So, I will try to keep it as simple and relevant as possible.

Let us take a metaphor to make things understandable. Imagine your body as a kingdom where enemies come from time to time to invade. Your immune system is the army and your immune cells are soldiers. Enemies are pathogen-like bacteria. Whenever the kingdom (body) is attacked by an enemy (bacteria), an immediate response is produced by our primary soldiers and guards (the innate immune system) on the doorways and halls of the kingdom. If the primary defense i.e. the less trained soldiers and guards fail to defeat the enemy force, a messenger of the king (दूत, here- Dendritic cells) quickly rushes to inform the king about the invasion and that it is getting serious. It does so by grabbing an enemy, chopping it into pieces and then reporting a few pieces of it to the head of the army (the adaptive immune system). But it doesn’t just directly present a chopped piece of the enemy as it is. It presents it on a special casket (the MHC Class II molecule).

Our immune system consist of two parts:

• The Innate Immune system &

• The Adaptive Immune system

Whenever the body is exposed to a foreign pathogen, it immediately starts a response by the innate immune system. The innate immune system is the first line of defense and is not specific. What this means is that the soldiers aka the cells of the innate system are like less trained but immediate-to- attack kind of pals. If the innate immune system fails to defeat the enemy force, it sends signals to the Adaptive immune system to send in more advances and specific fighters i.e.. the cells of the adaptive immune system. I am not going to name every defense cell and every mechanism, but only what is relevant. So whilst the innate immune system is fighting, dendritic cells come in and chop a few enemies and take those chopped parts called antigens to the adaptive immune system to check it out and then create antibodies and so on…..

An antigen is a piece of an enemy that your immune system can recognize.

Basically, our immune system has a very special molecule known as the Major Histocompatibility Complex class II aka the MHC class II. It is an antigen presenting molecule.

Everything that is made in our body is dictated by our DNA, and so are our MHC Class II molecules. The genes (part of DNA) that are responsible for the MHC molecules are the most diverse genes in the human gene pool, leading to a huge variety of MHC molecules between individuals. MHC molecules are surprisingly very unique to individuals.

Different types of MHC are better or worse at presenting antigens from different enemies, like one type might be especially good at presenting a specific virus antigen while another type could be great at presenting a bacteria antigen.

When Black death ravaged Europe in mediaeval times, there were people whose MHC class II molecules were just naturally really good at presenting the antigens of the bacterium Yersinia pestis, which caused the plague. These people had a higher chance of surviving and making sure humans as a species survived. This is so crucial for our species to survive to the extent that evolution may have made it a contributing factor in mate selection. Imagine if a close relative of the bacterium Yersinia pestis attacked the human race again. It could have the potential to wipe a great many individuals, had the MHC molecules not been inherited properly.

In human words: You find potential partners with MHC molecules that are different from yours more attractive! OKAY, WHAT?

How would anyone know this? I mean, if you meet someone suitable, you might like their physique or hair colour or any other desirable thing that evolutionary forces might make you want your progeny to have. But how will you make sure that they have an immune system with more diverse genes than yours, so that progeny created will have a great combination of genes to fight a more variety of pathogens?

The shape of your MHC molecules does influence a number of special molecules that are secreted by your body—which we pick up subconsciously, from the body odor of other people— so you communicate what type of immune system you have through your individual smell!

A popular German saying – “Jemanden gut riechen können,” literally translates to -“being able to smell someone very well,” which means “liking someone on an intuitive level.” This smell thing is a real thing! There have been an abundance of studies that showed that all sorts of animals—including humans—prefer the smell of mates with MHC molecules that are different from their own. We just find that if a potential mate has a different immune system, he or she smells sexier. This extra attraction is also a mechanism that avoids inbreeding. It also makes your biological siblings not smell attractive. By combining genes that create a diverse immune system, the chances of having healthy offspring rise immensely. So one of the reasons you may find your partner attractive is probably their immune system. So let that perfume not hide your allure.

PS: Evolution still doesn’t know the concept of hookup.

[1] Multiple researchers have debunked the idea throughout the years. When we talk about being attracted to the opposite, that might not comprise behavioral aspects.