The tricky relationship game is partly a biological affair

Chemistry of Love

If you randomly go out and fail to establish the necessary link with a supposed contestant to be your partner, do not worry. The explanation might be in your genes. Yes, that is it. More precisely, it is thought to be in your MHC - a large genomic region which is responsible for the immune system. It may seem completely odd, but, according to scientific evidences, this apparently innocent chromosome region may play a decisive role when one picks up a mate


By LUAN GALANI
from Curitiba, BRAZIL


Like in a well known modern physics law, the Coulomb's law, the opposites indeed attract each other in genetics. Scientists claim that people tend unconsciously to choose partners with very different genes of the immune system. Now, a Brazilian study from Federal University of Paraná assures that with results that were shown in a conference of the European Society of Human Genetics hold in Vienna, Austria.

The immune system is a biological tool that was shaped up by evolution to defend organisms against microorganisms' invasion, like viruses and bacteria. The performance of this system depends on the Major Histocompatibility Complex (MHC), which is a large chromosomal region that occurs in almost all vertebrate and has hundreds of various genes involved in.

Even today, researches are not aware of a region so extensively diversified of the genoma as the MHC, which is different in every single human. And this variability influences a major immunological resistence, which is an evolutionary strategy. Obviously, taking it at face value, it seems to be an overall advantage to humans, because the bigger the genetic variability, larger is the species' chance of perpetuation. Generally, the more diverse the MHC genes of the parents, the stronger the immune system of the offspring. But when it comes to transplants, variability is a dire drawback.

Anyway, what scientists from all over the world have discovered in the last decades is that females of any species decide for males that have the most different MHC from theirs. And researchers believe that women are not that different.

The sense of smell enacts a central role in this whole process. One of the hypothesis raised by the Brazilian study is that MHC molecules would partially be degraded and present in the corporal fluid evaporate, like if they were perfumes, and would be caught by smell receptors. According to the Brazilian team of scientists, the corporal smell is a whiff of identification. Through it we can identify genetically different partners. Similarly to feromonies that incite us to behaviors.

However, this smell is extremely subtle and humans may notice it only through a primitive nose connected to the limbic system (a cerebral region responsible for the process of emotion). According to specialists, more researches on it are needed to better understand this almost unnoticed smell.

The sweaty T-shirt study and nowadays

A prominent research suggesting MHC influences was first made by the biologist Claus Wedekind, in the University of Bern, Switzerland, in 1995, in which undergraduate students were issued clean white cotton T-shirts and told to wear them to bed two nights in a row. During this time, they were asked to abstain from - among other things - smoking, sex, garlic and deodorant. The day after the second night, the T-shirts were put into boxes, and a group of female college students was invited to sniff the shirts - each woman was given six of them - and rate the smells.

Overwhelmingly, the women preferred the odors of men with dissimilar MHCs to their own. Their preference yet was reversed if they were taking oral contraceptives. This famous experiment is better known as the "sweaty T-Shirt study". If not conclusive, it was at least provocative results.

And that was what inspired the Brazilian team to do the research which they analysed the MHC of 90 married couples and pointed out differences. The next step of the team of scientists is to investigate the facial morphology as other possible associated signal to MHC and the role of visual hints in picking up mates with different MHC.

Researchers recognise that attraction mechanisms in humans can not be reduced only to genetic patterns. Different from other animals, we have a set of cultural, behavioral and psychological factors that act on our choices. Therefore, decision about partners is not a genetic determinism, though biological components of choice can not be put aside. If he could, Darwin, wherever he is, would be sad. Sad to bits.


(Published: 20.08.2009.)