There has long been a debate about whether a person’s traits are gained through hereditary means (nature), or from the environment (nurture) that they grew up in. While I knew that a person does not get eye color or height from whether or not their parents took them to church, I found myself in the section of the population that believed that someone is who they are due to one’s experiences rather than a form of genetic predestination. Armed with my hypothesis I set out on a google adventure to see what science had to say…I found out that science disagrees.
I found two studies that powerfully refuted my belief: the first being the famous Minnesota Twin Family Study and a very compelling meta-analysis. This blog is going to focus mainly on the Meta-analysis due to its thorough process. The Meta-analysis was created by a collaboration of experts in the fields of neurology and gene speciality. The data was collected by taking 2,748 twin studies, published between 1958 and 2012, looking at 14,558,903 partially dependent twin pairs. The majority of these studies came from the United States, but studies were also taken from 38 other countries to insure punctiliousness. As well as ensuring variation in location of the studies, the twin pairings ranged in ages, but mostly focused upon twins between 18-64. These studies examined a total of 17,804 traits. The majority of these traits were categorized under 28 general traits. Out of these 28, ten were investigated: temperament and personality functions, weight maintenance functions, general metabolic functions, depressive episode, higher-level cognitive functions, conduct disorders, mental and behavioral disorders (due to use of alcohol), anxiety disorders, height, and mental and behavioral disorders (due to use of tobacco). The study found that while genes were not the sole cause of all traits, there was not a single trait studied that genes did not affect in someway. The amount that the genes controlled traits varied from case to case, but on the whole it was found that traits either influence, or completely control each trait. While this study alone showed me that my beliefs were wrong, I continued to search for a different study to investigate where normal behaviors come from, rather than disorders and complex traits. In my search I found The Minnesota Twin Family Study.
This study was a longitudinal study done on twins and parents that were separated at birth. To my relief, an interview with one of the scientists involved in the study, Nancy Segal, admitted to originally believing some traits, such as religious beliefs and social attitudes, would be effected by nature not genetic influence at the get go of the experiment. Unfortunately for both of us, through the study, the findings show that genes in fact do play a role in behaviors such as these. Although this study again proves that I was wrong. With Andrews lecture on the Texas Sharpshooter problem and the file draw problem fresh in my mind I began to become skeptical the more I read. As I read the articles and results they seemed to focus on amazing accounts of twins that were separated at birth and still had amazing parallels between their lives, for example: two twins who had the same names, same habits, drove the same car, and went on vacations to the same beach. The articles only talked about incredible cases, and in my mind I could not shake the thought of where all the boring, or normal studies were. While I had these doubts the evidence provided by these two studies could not be proven wrong.
In conclusion, these studies showed me, with overwhelming evidence, that my hypothesis was wrong. The evidence of 14 million twins proved to me that it is in fact nature that prevails when it comes to personality traits, not nurture as I once believed.
Lewis, Tanya. “Twins Separated at Birth Reveal Staggering Influence of Genetics.” LiveScience. TechMedia Network, 11 Aug. 2014. Web. 21 Oct. 2016.
Miller, Peter. “A Thing or Two about a Thing or Two, A.k.a. Science.” National Geographic 24 (2013): 59-62. Web. 21 Oct. 2016.
Polderman, Tinca C J, Beben Benyamin, Christiaan A. De Leeuw, Patrick F. Sullivan, Arjen Van Bochoven, and Peter M. Visscher. “Meta-analysis of the Heritability of Human Traits Based on Fifty Years of Twin Studies.”Nature Genetics. Nature Publishing Group, 18 May 2015. Web. 21 Oct. 2016.