Are our personalities and behaviors determined by our genes or shaped by our environment?

Drawing on Edison’s famous aphorism, we examine whether human personality and behavior are more strongly influenced by genes or the environment. While genetic determinism and environmental determinism have long been pitted against each other, epigenetics emphasizes that the two interact.

 

Edison’s quote “Genius is 1% inspiration and 99% hard work” is a very famous aphorism. While it’s believed that Edison actually said this to emphasize the 1% inspiration, many people take it to mean that hard work is crucial to success. However, from a scientific perspective, it’s worth considering whether Edison’s original intention was correct, or whether the current meaning is more appropriate. This goes back to the question of whether human personality traits and abilities are innate or acquired.
Even before the discovery of genes, there were many theories about the formation of human personality. Some theories emphasize the importance of the environment in shaping a person’s development, while others emphasize the importance of heredity, as in the saying “sons are like their fathers”. The fact that these theories have coexisted for so long is due to the fact that there are many examples to support each position.
First, environmental determinists, who argue that the environment plays an important role in determining personality, offer the following evidence. For example, identical twins who are genetically identical will not have a 100% match in personality or abilities if they are raised in different environments. In fact, one study found that when one identical twin is homosexual, there’s about a 50% chance that the other will be too. In another study, only one of the identical twins was found to have the genetic disorder Russell Silver Syndrome. If genes unconditionally determine personality and health, these examples would not be possible. Therefore, environmental determinists argue that a person’s personality and health are not dependent on genes, and that personality and health can be changed through psychotherapy or new environments.
However, there are examples that contradict this claim. For example, twins who were each adopted as infants and reunited 40 years later and both became weightlifters, or people who grew up in different environments but have nearly identical favorite subjects, smoking and drinking habits. It’s hard to explain these cases as mere coincidence to those who claim that environment determines everything, and even if there is not a 100% chance of being gay, there is undeniably some correlation.
On the other hand, there are genetic determinists who argue that genes play an important role in determining human personality and behavior. This is a relatively new theory that has gained momentum as the structure of the human genome has been unraveled. Genetic determinists argue that personality and behavior are determined by genes, citing the counterexamples to environmental determinism mentioned above. The idea is that it’s not a coincidence that identical twins share the same occupation, hobbies, or amount of alcohol they drink, but rather the inevitable result of their genes.
The idea that genes determine our dispositions is supported by research on the MAOA gene. Han Brunner from the Netherlands found that people with a short MAOA gene have problems controlling anger, which leads to violence. This suggests that a short MAOA gene is a gene that symbolizes violence. Furthermore, in his book The Selfish Gene, Richard Dawkins argues that humans are merely tools used by genes to thrive, and that all human behavior is programmed by genes.
However, the idea that all of our behavior is determined by our genes has been called into question because the number of genes is lower than expected. Humans have been found to have about 20,000 genes, but this number seems insufficient to explain all human traits. The fact that identical twins can differ in the expression of genetic diseases also shows the limitations of genetic determinism. The claim that genes completely determine human behavior denies the free will of individuals and raises ethical issues, such as treating people as potential criminals or patients.
Epigenetics is a field of study that aims to address these issues. Epigenetics argues that the same genes can lead to different personalities and behaviors depending on whether or not they are expressed. For example, worker and queen bees have the same genes, but the gene that makes a queen bee is expressed by an external factor called royal jelly. This can be seen as a position that encompasses elements of both genetic determinism and environmental determinism.
In the end, we can say that both environment and genes play a role in determining human behavior, but genes play a more important role. If identical twins are not 100% identical, it is only a matter of gene expression, and if the conditions for expression are met, they are likely to have the same tendencies. Even if the number of genes is small, the complexity of each gene is sufficient when considering the possibility of its expression.
Therefore, once the mechanism of gene expression is understood, the ethical issue can be resolved to some extent. The mere presence of a gene does not make someone a violent person, and if we can find a way to prevent its expression, we can prevent potential problems.
In conclusion, genes have the greatest influence on human behavior. We don’t yet know the role of each gene or the conditions under which it is expressed, but when we do, we will have a deeper understanding of human nature. Thus, Edison’s adage, “Genius is 1% inspiration and 99% hard work,” can be interpreted to include both genes and their expression conditions.