Similarity ≠ Compatibility? How Biology Works Against Incest
From bad kisses to repelling scents, your genes may be the reason behind failed chemistry — nature’s way of protecting humanity from inbreeding
Imagine this. You're on a date, and it's going amazingly. The conversation is flowing, the food is delicious, and the person is super fun. Now you've almost reached home, and now comes the moment you've been waiting for - the first kiss. You look into each other's eyes, slowly lean in, and kiss. And it sucks. Everything was objectively right, but somehow didn't sit well.
However, it's not just amicability that determines sexual compatibility; genetics play a significant role in who we pick as our partners. The human body has in-built mechanisms that repel others with similar genes - especially in romantic or sexual contexts - to avoid inbreeding. This concept is based on a group of genes known as the Major Histocompatibility Complex (MHC).
"It may be tempting to think that humans choose their partners because of their similarities," Maria da Graça Bicalho, a professor of immunology at the University of Paraná in Brazil, told The Guardian. "[But] our research has shown clearly that it is differences that make for successful reproduction."
Numerous studies have shown that humans prefer to mate with individuals who have dissimilar MHC genes. In 1955, an experiment was conducted where women were asked to smell T-shirts worn by different men over the course of several days. It was found that women consistently preferred the scent of men with different MHC genes from their own.
In another 2005 experiment, it was found that women found the faces of men with dissimilar MHC genes more attractive than those with similar MHC genes. This biological mechanism can be seen as a strategy to produce offspring with a diverse immune system, increasing their chances of survival.
Every part of our body carries traces of DNA, including bodily fluids such as sweat and saliva. So when someone's kiss or smell feels off-putting, that could be a sign of genetic similarity and, in turn, incompatibility.
But genetics don't impact sexual attraction alone. Even when two people have lived in close, domestic proximity to each other during early childhood, they might become sexually desensitised to each other despite not being genetically related - a phenomenon known as the Westermarck effect.
When individuals grow up together, like in the case of Israeli communal peer groups or Chinese minor marriages, they become sexually averse to each other and subsequently, unable to rear children.
"We expect to find that cultural aspects play an important role in mate choice, and certainly do not subscribe to the theory that if a person bears a particular genetic variant it will determine his or her behaviour," Bicalho explained to The Guardian. "But we also think that the unconscious evolutionary aspect of partner choice should not be overlooked."
Genetic compatibility plays a significant role in healthy reproduction, ensuring that children grow up strong and able.
Next time you're repulsed by a potential lover's taste or body odour, perhaps think twice about whether the relationship is worth compromising your bloodline's immunity system.
