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Are Our Personalities Pre-Determined?

Author: Winnie Mok

Editors: Misha Wichita and Jason Zheng

Artist: Lalita Ma

Psychologists have long been fascinated by the age-old question of whether nature or nurture has a greater effect on personality. If genetics dictate our personalities, our behavior would have to be the same throughout our lives, but that is not necessarily true. On the other hand, if our environment contributes more to how we act, our personalities are more susceptible to change depending on our experiences. To delve into this debate, we must first understand what personality is. 

Personality encompasses all the unique traits that make up a person’s behavior. No definitive study has succeeded in quantifying the exact number of personality traits due to the nearly endless possibilities. Take, for instance, psychologist Gordon Allport who has identified more than 4,000 types in a list of personality traits he created. The sheer amount of traits indicates that personality is not determined by a single gene but is instead the result of the interactions of numerous different genes. Yet, even the combined effort of multiple genes is not enough to control our personality, as some genes only manifest in specific environments, highlighting the interplay between genetics and environments in forming our personalities. 

However, this is not to say that genetics can be entirely disregarded when shaping our personality traits. Twin studies, which examine genetic and environmental influences on personalities between twins, have revealed that identical twins are more likely to exhibit similar personalities than fraternal twins, displaying that genetics do play an important part in the development of our temperament. This conclusion stems from the fact that identical twins share the same set of DNA while fraternal twins share only half. Suppose the environment is the key factor in determining personality, regardless of whether a pair of twins are fraternal or identical. In that case, twins should be equally similar, given that they are raised in the same household. On the other hand, identical twins raised separately should be more temperamentally different than their counterparts raised in the same household. One example disproving this belief is the “Sources of Human Psychological Differences: The Minnesota Study of Twins Reared Apart,” paper published by Thomas J. Bouchard and his colleagues in 1990. In this study, scientists compared both identical and fraternal twins who were reared apart and reared together. They found that the IQ scores between the identical twins raised separately were consistent with those who were reared together. Similar results were shown in the twins’ behaviors, religion, and interests, leading the scientists to conclude that the environment does not affect the similarity between identical twins. To explain these results, Bouchard et al. claimed that genetic factors exert control over environmental factors as the twins will naturally be drawn to specific environments due to their biological composition. The role of genetics in determining personality is also seen in the difference between fraternal and identical twins. Characteristics such as aggression and the likelihood of divorce had a stronger correlation among identical twins than fraternal twins who were raised together. 

While genetics undoubtedly play a significant role in shaping our personality, we must also recognize the influence of environmental factors such as culture, community, education, and geographic location. Contrary to what the media might portray, there is no gene directly responsible for intelligence or being a good partner. Certain genes may lead to a higher chance of developing specific traits, but the environment we are raised in can allow or prevent the fruition of these behaviors. 



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Twins Reared Apart” (1990), by Thomas J. Bouchard Jr, David T. Lykken, Matthew

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Mõttus, René. “Why Personality Is Not Genetically Hardwired.” Psychology Today, 19 Oct.

Stangor, Charles, and Jennifer Walinga. “12.3 Is Personality More Nature or More Nurture?

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Accessed 29 Mar. 2024.

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