Can your blood group determine your personality? A genetic insight into introversion
Extensive research on personality traits has shown that introversion is 50% heritable, meaning that half of the differences between extraverted and introverted personalities are due to genetic differences. However, it was not until 2021 that researchers were able to find empirical evidence for the association between the introversion trait and a specific gene, that is the ABO blood group gene (Hobgood, 2021). While these findings are very recent and have yet to be replicated and validated, they are particularly exciting due to their strong biological foundation and have the potential to not only change how we study and view introversion and personality traits but also the way we predict and cure several pathologies.
But let’s first have a look at how introversion originates and why it could be related to our blood group.
A brief overview of introversion
Introversion is considered the opposite of extraversion, which is one of the globally recognised Big Five personality traits, originally identified by Eysenck. Introverted individuals are estimated to be 20-40% of the world population and are generally defined as oriented toward their inner thoughts and feelings, rather than the external environment (Walker, 2020). This personality trait largely affects one’s behaviour, leading introverts to appear as more reserved, quiet, passive, and less prone to social interactions compared to extroverts.
While the optimal level of extraversion is still up to debate and it is assumed to vary from person to person, research has found that highly introverted individuals tend to have negative repercussions on their physical and mental health (Lukaszewski & Roney, 2011). More specifically, extreme introversion has been linked with widely diffused illnesses whose causes are still unclear, such as depression, generalised anxiety disorder, attention deficit disorder, autism, and many others (Hobgood, 2021).
For this reason, several researchers believe that a greater understanding of introversion could allow us to better prevent and treat such illnesses. However, it is first necessary to understand how introverts and extroverts differ on a biological level.
Dopamine, the ABO gene, and associated diseases
Over the decades, researchers have found that introverts and extroverts mainly differ in their level of arousal, with introverts being chronically more aroused than extroverts (Rammsayer, 2004). For this reason, introverts tend to make limited use of dopamine, a neurotransmitter that provides the motivation to seek external rewards, such as reaching a certain social status or earning money, which would lead to an overstimulation of the already highly aroused nervous system of introverts (Granneman, 2015).
While dopamine is regulated by several factors, DBH (dopamine beta-hydroxylase), located on chromosome 9q34, is one of the main enzymes responsible for the conversion of this neurotransmitter. Because of its physical closeness to the ABO blood group gene position, several studies have suggested that the activity of DBH could be regulated by the ABO gene (Craig et al., 1988). However, Hobgood (2011) was the first to suggest that, due to the tight connection between extraversion levels and DBH, the ABO gene would also be an important determinant of the level of one’s extraversion.
While a link between personality traits and the ABO gene had been previously suggested, research in this field is extremely limited and controversial, as personality traits have been studied in relation to blood groups by several controversial and non-scientific groups, such as the Nazi, who believed that the ABO B blood group was associated with lower instincts and frequent in Asian and Jewish individuals (Tsuchimine et al., 2015). However, it is important to understand that heritability is a measure of variation rather than causation and its effects constantly decrease and increase with changes in our environment. Hence, genes do not predetermine who we are, but rather predispose us to behave in a certain way and we should not be afraid of learning about these predispositions!
Furthermore, Hobgood’s research is in line with several medical studies that show an association between illnesses such as depression and anxiety, previously described as closely related to introversion, and various diseases linked to DBH, including cancer, cardiovascular disease, and stress response-related immune disease (Reiche et al., 2004; Tsuchimine et al., 2015). While these links are only a part of the bigger puzzle that leads an individual to develop such illnesses, what if, in a not-so-far future, you could prevent someone from experiencing major depression and cancer just by testing for their blood group?
But how do we know what blood group is associated with introversion?
The ABO AB blood group
Eysenck (1982) was the first to suggest a link between introversion and the AB blood group and several other studies have found empirical evidence confirming that this link exists. Among many, Gupta (1990) demonstrated that individuals with an AB blood group were the least sociable, the least impulsive and the least extraverted, Nahida and Chatterjee (2016) found that they had the lowest mean of “openness” and Asgari (2015) showed that they had the highest tendency to work individually, all typical characteristics of introverts. Nevertheless, since several other studies failed to replicate these results, most researchers hypothesised that a link between introversion and the AB blood group did not exist (Rogers & Glendon, 2003).
Hobgood’s (2021) recent research, however, was able to revolutionise the way the ABO AB blood group is tested and explain the inconsistent replication of findings. The researcher suggested that, since the ABO AB blood group is composed of two antigens, the ABO A antigen and the ABO B antigen, one of the two must have a greater contribution to the development of introversion (See Figure 1). This would explain why previous studies did not always find statistically significant results: due to the several genetic mutations over the decades, people sharing the same blood group (which in this case is the AB blood group) may have slightly different antigens and, consequently, differ in their level of introversion.
Figure 1: Antigens in the ABO blood group cells
ABO blood group system. (2022, August 6). In Wikipedia.https://en.wikipedia.org/w/index.php?title=ABO_blood_group_system&oldid=1102769320
To prove this hypothesis, Hobgood dissected the ABO gene into the two antigens by comparing blood groups of 225 obstetric patients and found that, among patients with the AB blood group type, the ABO B antigen was responsible for 56% of the introversion trait, the ABO A antigen of 51% and, together the ABO AB group was responsible for 54% of the introversion trait. Hence, the researcher concluded that the ABO B antigen was the main driver of introversion in the ABO AB group and explained that future studies should analyse the B antigen in isolation in order to determine whether a link with the introversion trait exists.
Conclusion and implications
The present article challenges existent prejudices on the study of genetics in relation to personality traits by providing empirical evidence that a direct link between the introversion personality trait and the ABO AB blood group, more specifically with the B antigen, exists. Nevertheless, Hobgood’s (2021) research is very recent and findings should be replicated in order to obtain greater validity.
Finally, other studies have recently suggested that other genes could be correlated to introversion and that the ABO gene could also be linked to other personality traits, suggesting that we are still at the beginning of our journey into the understanding of genetics. (Kanazawa, 2021; Tsuchimine et al., 2015).
References
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