Genetic variants linked to human personality have been identified

The article by Schwaba and his team represents a significant step forward in our understanding of the role of genetic factors in human behaviour. Personality traits — in this case, the so-called ‘Big Five’: neuroticism, extraversion, agreeableness, openness to experience and conscientiousness — have long been the exclusive domain of research from a purely environmental perspective. However, quantitative genetic analyses (twin and family studies) had already been providing evidence for decades pointing to a moderate role for genetic factors (heritability of 30–50 per cent) in the variability of these traits, which influence how people think, feel or behave.

This study follows a line of research complementary to classical analyses, which has been developing in recent years, by conducting a genome-wide association study (GWAS) for the five main personality traits mentioned above. Whilst it is not the first of its kind, it does achieve a level of statistical power and methodological rigour far exceeding anything achieved to date. The participation of 46 cohorts from different countries, with a combined sample of between 600,000 and 1.4 million people, represents a colossal effort that has enabled the identification of associations between these traits and 1,260 genetic variants. Furthermore, these detected associations are consistent across different geographical regions, data sources, age groups and measurement instruments, and appear to be largely independent (82 per cent) for each of the traits studied. The use of a wide range of complementary analyses has enabled the authors to conclude that the genetic architecture of personality is robustly generalisable and minimally affected by confounding factors, such as the family environment. Taken together, the results continue to confirm the model according to which the genetic influence on human behaviour occurs via a large number of genes, each of which has a minuscule effect at the individual level, but a significant one when considered collectively.

However, whilst this is, as it stands, a magnificent piece of research, it is far from being the answer to all questions, nor is it the promise of predicting behaviour from DNA—a notion that always lurks, in biased or misinformed interpretations, behind published advances in behavioural genetics. The method itself has limitations inherent to our current technical and methodological capabilities: the variants studied (Single Nucleotide Polymorphisms, SNPs) are merely a sample of the variability that can be found in DNA and cannot account for the possible role of gene interactions, meaning that the variance explained in this way will always be limited to what can be explained by purely additive effects (heritability based on SNPs ranging from 7.4 to 10.6 per cent in this case). Consequently, the predictive power of polygenic indices (PGI) —the individual score obtained by summing the weighted effects of all the variants involved— is very limited; whilst of great interest from a research perspective, it has little practical relevance. In other words, it would clearly be erroneous (and the authors themselves emphasise this) to interpret these results as supporting deterministic biological models or to propose direct real-world applications.

Finally, whilst the study focuses on analysing the role of genetic factors, this does not mean it overlooks the extremely important role of environmental factors in personality traits. Whether on their own or in interaction with genetic factors, each person’s life experiences will always have a significant impact on the shaping of what we call personality.

In short, this is a major endeavour of extraordinary interest, but one that reminds us how much further we still have to go in this field and how easy it is to misinterpret (by either over- or underestimating the results obtained) the extremely complex relationship between genetic factors and human behaviour.