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A while ago, in Psychology class, our teacher’s daily lecture was on the classic psychological debate of Nature versus Nurture. Do our genes impact our personality or are we an Aristotelian tabula rasa, or blank slate? While a connection could be seen inherently through this psychological concept’s usage of biological premises, a connection was easily seen between Psychology and Biology after my teacher displayed a Punnett Square, a common sight in genetics as a way to explain the transfer of genotypes from parents to offspring. As I recalled previous lessons from Freshman year on genetics, I couldn’t help but contemplate whether or not the theory had any validity.
Dr. Michael Kraus, assistant professor of Organizational Behavior at Yale, says it’s complicated. Historically, he said, psychological studies would focus on twins, and compare self-reports from fraternal twins, those of which share around 50% of the genes, and identical twins, who share 100% of their genes. In these studies, they found that the amount of variation in personality that is explained by genes, or heritability, was around 46% for identical twins, and around 23% for fraternal twins, showing a very clear suggestion that genetic influences had a noticeable impact on personality. The problem is finding what genes specifically impact factors like personality, preferences, intelligence, or physical characteristics.
Excited by the new ability to sequence the entirety of the human genome, Dr. Kraus says that scientists have now been attempting to discover distinct sequences of repeating DNA to identify a version of a specific gene. Many of these genes have been discovered, and have made dramatic impacts on the medical and biological fields, such as APOE4, which has been linked to increased risk of Alzheimer’s Disease, or rs53576, which is associated with increased oxytocin receptors in the brain. However, in every breakthrough finding a linkage with a specific gene sequence to a personality characteristic, there was a null replication, as these studies failed to adequately replicate previous results. These studies suggested that in fact we do not have specific genes for personalities. But what about those twin studies that had originally shown a connection between genetics and personality types?
Dr. Kraus has said that even though no studies have been adequately able to replicate their findings, there’s still promising new studies coming up. One study is attempting to associate sequences of DNA associated with dopamine in relation to sensation seeking behavior. The study has been able to show genetic influences for addiction that will have great impacts in the medical field and in preventative measures in geneticism. These studies however only have, a 6.6% heritability, which is a far cry from the 46% from the twin studies. The lack of evidence for biological influences on personality are not due to refutations, but due to the recency of the entire sequencing of the human genome, and lack of ability to fully study these all of these genes (scientists are still in the process of going through all 50,000 related to dopamine itself).
So is our personality decided by genetics? It is likely that certain parts can be, but without substantial evidence, we are still in the dark. Over time, however, with new discoveries in relation to the human genome, we should see some noticeable developments in biology, psychology, genetics, and medicine. Until then, the debate is merely philosophical.