The biological mechanisms of infidelity
It is possible that there is a phylogenetic predisposition of the brain to infidelity relationships, which is also important for adaptive purposes (Buss, 1994). It is in fact undoubted how, both in the human and in the animal species, the males and females who manage to find a greater number of partners more or less internal to the couple, have always had a greater possibility of reproducing and therefore of continuing their own species .
Advertising message It is customary to indicate the concept of marital fidelity as a value, that is, a moral and intellectual gift that constitutes an expression of an individual’s personality and evolutionary context. Being faithful is therefore an attribute, a modus vivendi that can derive not only from the individual’s thinking and behavior habits, but also from the cultural, religious and social conditions of the environment in which the person evolves and lives, interacting with their own kind. That moral values have a close correlation with culture certainly does not constitute an element of novelty: it is clear how in a society a behavior can be defined as unfaithful which in a different cultural structure is characterized by absolute normality, and nothing at all stigmatized (see for example the case of monogamy in Eastern and Western societies, or the case of adultery foreseen as a crime in some countries of the world, while in others stigmatized only as amoral conduct but without any legal consequence). What constitutes a novelty, on the contrary, is to affirm that marital fidelity, understood as the ability to create and maintain a stable and long-lasting bond with one partner over time, can derive, both in animal and human species, also from factors biological, hereditary and, therefore, innate. To support such a thesis also means to accept that certain individuals, by virtue of certain neurobiological characteristics, can naturally be predisposed to fidelity with respect to others who do not exhibit the same characteristics. Some recent scientific studies have shown that in reality, in this apparently improbable statement, there is some truth. Some of the most significant conducted in this field are mentioned.
First of all, we anticipate that the neuronal vasopressin hormone plays a fundamental role in some human processes aimed at cooperation and collaboration in the couple; specifically, its presence, together with that of oxytocin, is significantly increased in the establishment of the attachment phase, which immediately follows the period of falling in love, in which peptides such as serotonin, adrenaline and dopamine are the masters. Oxytocin is a hormone that is released by men and women during orgasm, and by women during childbirth and breastfeeding; it is also a hormone that plays a fundamental role in establishing attachment between mother and child.
While oxytocin acts primarily on the maternal dyad, vasopressin appears to play an important role in the couple’s attachment phase. In addition to regulating the pressure, this hormone is responsible for post-orgasmic satisfaction, determining the degree of loyalty to the partner. The quantity of this hormone within a subject, both human and animal, is determined by the type of alleles related to the vasopressin system which, where affected by polymorphism, are shorter and less able to actively respond to the substance. This causes a lower production and a lower sensitivity of the receptors to the same, effects that translate into behaviors less prone to loyalty and attachment to the partner.
This is evidence found primarily in animals, given that in some particular species of rodents, for example voles, it has been seen that a more massive presence of the vasopressin hormone is positively related to loyalty to the partner, and therefore to monogamy; moreover, these are species where a polymorphism of the alleles relating to the vasopressin system has been found (Hammock and Young, 2002).
Men carrying a specific allele of the vasopressin gene underwent an evaluation study by Walum and colleagues (2008): they were married or living together for five years or more – 552 couples overall – to whom Parent was administered Bonding Scale, aimed at assessing attachment to one’s partner. The results were explicit: subjects carrying this specific allele showed less attachment to their partner, and their scores were also dose-dependent: those who owned two of these alleles showed less attachment than those who only had one. in turn followed by those who did not present him at all. The men carrying this allele also had major couple crises in the previous year, including threats of divorce and removal from the marital home, and also in this case the scores turned out to be dose-dependent, because men with two copies of the allele showed twice the probability of having had a couple crisis in the 12 months previous than those with a single copy or with no copy of the allele, and a greater number of extramarital relationships compared to the comparison groups. Finally, the wives of men carrying one or two alleles showed significantly lower scores on the questionnaires aimed at detecting the degree of marital satisfaction because men with two copies of the allele showed twice as likely to have had a couple crisis in the previous 12 months than those with a single copy or with no copy of the allele, and a greater number of extramarital relationships than comparison groups. Finally, the wives of men carrying one or two alleles showed significantly lower scores on the questionnaires aimed at detecting the degree of marital satisfaction because men with two copies of the allele showed twice as likely to have had a couple crisis in the previous 12 months than those with a single copy or with no copy of the allele, and a greater number of extramarital relationships than comparison groups. Finally, the wives of men carrying one or two alleles showed significantly lower scores on the questionnaires aimed at detecting the degree of marital satisfaction
But what is the allele identified by Walum? Is there really a genetics of loyalty, then? It would be specifically the AVPR1A gene, located on chromosome 12q14-15, whose polymorphism sequences would not be correct and continuous. The polymorphism of this gene has been correlated with autism, with early and multiple sexual behaviors, and finally with less altruism and prosociality, testifying to how it has a significant impact on human behavior.
Another study recently conducted by Garcia and colleagues (2010) on 181 adult men, has shown that there is a direct link between specific alleles of the dopamine system and greater frequency of occasional sexual intercourse, and therefore outside of a relationship, as well as greater frequency of sexual infidelity. Remember, in fact, how the dopamine system is strongly connected with the reward system and the search for novelty, aspects that can be strongly involved in the behavior of promiscuity and sexual infidelity. Specifically, it is believed that genes that mediate dopaminergic transmission, especially the gene for the D4DR receptor, are associated with the search for new stimuli, including sexual ones, especially when they have seven or more allele sequences. A greater lengthening of these alleles could in fact predispose to impulsive behaviors, the search for new stimuli, and, specifically sexual behavior; subjects with 7 or more repeats of the D4DR allele have been shown to be more likely to have occasional relationships, even in the absence of significant differences in overall fidelity (Garcia et al., 2010)
An additional biological system involved in loyalty appears to be the immune system. In particular, the reference goes to the major histocompatibility complex (MHC), a group of polymorphic genes consisting of 30 units located on the short arm of the human chromosome 6. The typical histocompatibility system of these cells is based on the molecules present in the membrane of the the same which, in contact with a person’s immune system, recognize it as a foreigner and, by adopting an immune response, act as antigens: in a nutshell they bind to the foreign molecule and try to counter it.
This is a procedure that is at the basis of the compatibility check for organ transplantation which, in case of immune refusal, better known as rejection, cannot be implemented. Instead, in this case, the immune systems of the donor and the donor are required to be afferent and similar, perhaps because they are linked by kinship or intrinsic genetic affinities: people with a similar MHC are in fact probably related.
Advertising message This recognition mechanism, in humans, is activated with the simple use of smell: thanks to the emission of pheromones, which carry traces of the molecules of the MHC system just described, it is possible to recognize a genetically similar subject to yourself from someone who is not. It is a biologically innate system, most likely developed over time by humans to avoid incest, according to the Wedekind hypothesis (1995). Subjects who “smell” the same molecules of their own MHC in another, tend to avoid it as a partner because they unconsciously recognize it as a relative; the opposite behavior occurs on the contrary by identifying subjects with genetic heritage different from their own, who are massively chosen as sexual partners,
Wedekind confirmed, with the famous experiment of sweaty T-shirts, how women are inclined to choose partners with different genetic heritage than their own, and how recognition of the same is possible simply by smelling the sweaty T-shirts of the aforementioned males. The sweat, soaked in pheromones, is sufficient to identify a foreign subject, reassuring the woman about the risk of having sexual relations with potential relatives.
Wedekind’s studies have been replicated around the world several times, and have always led to the same results, thus demonstrating the validity of the starting hypothesis. In particular, one of these studies showed that women married to men who had genes similar to theirs in the MHC component of the immune system also appeared more prone to adultery; moreover, the more these genes were shared between a woman and her spouse, the more inclined the partner was to maintain extramarital sexual relations (Garver-Apgar et al., 2006).
The structure of the brain has also been found to contribute to infidelity; in particular, reference is made to the three brain systems which, according to Fisher’s hypothesis (1998), were developed by man for the performance of specific tasks and functions: that of sexual attraction, linked to the hypothalamic system, such as the physiological sensations of hunger and thirst, that of romantic love, referring to the reptilian system, an archaic brain area to which the satisfaction of instincts connected to survival is linked, and that of romantic attachment, dependent on the area of the pale ventral, linked in turn to sensations of taste and pleasure. These three neuronal systems have numerous interactions with each other and also with many other brain systems, and are capable of generating a wide range of thoughts,
Despite this, they can also act separately, causing in this case a sort of division between the functions to which each of them is connected, functions which thus manifest themselves and make themselves explicit independently of each other: few words you can feel physical attraction for a person outside the couple, while feeling attachment for a certain person, perhaps a permanent partner, and romantic love for another person (Fisher, 2004). This profoundly scientific and biological explanation could constitute a valid response to human behavior, especially male behavior, which very often finds itself manifesting the three needs identified above in a split and contemporary manner.
The biological independence of these three neuronal systems would also have allowed, since the time of Homo sapiens, to have an official monogamous relationship and at the same time to conduct clandestine sexual relations (Fisher, 2004). Hence a possible phylogenetic predisposition of the brain to infidelity relationships, also important for adaptive purposes (Buss, 1994). It is in fact undoubted how, both in the human and in the animal species, the males and females who manage to find a greater number of partners more or less internal to the couple, have always had a greater possibility of reproducing and therefore of continuing their own species .
Here in infidelity an innate intent to contribute to one’s own fitness could be hidden, aimed at bringing the reproductive benefits of a genetically more varied offspring (Fisher, 1992). Infidel males could in fact have had greater possibilities of reproduction thanks to a greater number of sexual relations conducted outside the couple, and females, for their part, may have obtained from clandestine sexual relations, a greater number of resources available and parental support for the offspring after the death of the first partner or abandonment by the latter (Fisher, 1992). Therefore, clandestine infidelity may have had the merit of bringing reproductive advantages to ancestral females and males no less than monogamy itself,
Not only an ethically incorrect behavior, therefore, would hide beyond the clandestine unfaithful relationship: science suggests how the predisposition to infidelity, both in males and females, can not only boast biological and therefore innate origins, not learned and genetically heritable, but may even prove useful, if not valuable, for the reproduction and maintenance of the species.