In a detailed analysis, Laurie Clarke examines the complex forces that shape personality and how new research is profoundly changing our understanding of the role of genes.
A 2009 case in Italy is one of the most controversial examples: Abdelmalek Bayout, convicted of murder, managed to have his sentence reduced after his lawyer argued that his DNA contained the MAOA variant, known as the “fighter gene,” linked to aggressive behavior. The argument was partially accepted by the court. But today, science considers this approach too simplistic.
Since the 1990s, studies have shown links between certain genetic variants and behavior, but research over the past 15 years has debunked the idea that a few single genes determine personality. According to researchers, human traits are polygenic – influenced by thousands of small variants throughout the genome, each with a minimal effect.
Twin studies also show a more complex picture: identical twins are more similar than fraternal twins, but their personalities are never the same. A large 2015 analysis found that about 47% of personality differences are related to genetics, with the rest due to environment.
However, even environment does not have the decisive influence that is often attributed to it. Studies show that major life events – even traumatic ones – leave much smaller traces than previously thought. Even factors such as education, marriage or parenting have only a limited influence on the formation of personality.
Recent research suggests that personality is a combination of polygenic and polyenvironmental factors: many genes and many small life experiences interact to shape the individual. Furthermore, the environment can also influence how genes themselves are expressed, activating or deactivating certain tendencies.
Despite major advances in genetic studies, scientists acknowledge that we are still far from fully understanding how personality is formed. But one thing is clear: neither DNA nor life alone determines who we are – our identity is the result of a much more complex interaction than previously believed.
