The Relevance of Twins on the Nature vs. Nurture Debate

Grace McClung and Nina Dorighi, Journalists

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Does one’s experience with life impact who they become more than the genes they were born with? This is an age old question posed to countless people that has become a debate known as Nature vs. Nurture. Scientists and psychologists use twins to explore this debate because of the genetic similarity between the siblings. Infamous cases like the Jim Twins and the Louise Wise Case help scientists learn even more about the influences of environment and genetics. With twins ourselves, we are interested in understanding how twins play a part in the study of human development.

Twin studies have been around for a long time due to the genetic marvel that lies within the siblings. However, some cases of these studies are mind boggling and some argue inhumane. In the Secret Sibling case, Doug Rausch and Howard Burackand had both been adopted through Louise Wise Services in the 60’s. ABC News reports that George Rausch was told he would not be able to adopt Doug if he couldn’t participate in a study. After he agreed, the adoption agency gave them their new son. Both Rausch and Burack and their families reported mysterious researchers coming to their homes to conduct tests, interviews and film the boys in their childhood. Doug Rauch told “20/20” that they even filmed him riding his bike. The families reported the researchers visiting the boys for a decade. It wasn’t until the twins were grown adults when the truth was exposed. At the closing of the Louise Wise Services, a guilty woman dying of cancer called Doug to reveal that he had a long lost twin. Eventually they met and were able to rekindle their relationship. It turned out the researchers were conducting a study on nurture vs. nature and using the boys as human test subjects. After the truth was displayed for the public many people thought the study was inhumane. To separate siblings, let alone twins at birth changed their lives. That’s the difficulty when exploring nature vs. nurture on twins, there’s not a way to do it accurately without having to go that extra step and isolate them from one another. 

The term “nature” explores the idea of genetic similarities and heritable traits. There are two types of twins: fraternal (dizygotic) and identical (monozygotic). Fraternal twins result from two different eggs and therefore share only 50% of their genes. Identical twins result from one split egg which is why they share 100% of their genes. This difference is important because identical twins are more likely to be affected by genetics and provide more support for the nature side of the debate. In the case of the Jim twins, the influence of genetics on their behavior is undeniable. In 1940, two twin boys had been put up for adoption and their adoptive parents named them both James at just three weeks old. As they grew up 40 miles away from each other, the list of their uncanny similarities continued to grow. Both James became Jim for short and they each lived with a dog, both named Toy. As children, they excelled at math and woodworking but struggled with spelling. And as they shifted into adulthood, their lives were nearly as similar as their DNA. Both Jims married twice, first to a woman named Linda and second to a woman named Betty. Both smoked, drove the same car, and worked similar jobs. When their first child came along, the Jims both named their son James Allan. They even liked to vacation in the exact same spot in Florida. Are these all just coincidences? Probably not. Twin studies have suggested that these strange similarities are the result of genetics. They support the first rule of behavioral genetics that psychological traits are extremely heritable, about 50% on average according to Simply Psychology. The same studies have also proved there are correlations between twins on a range of behavioral traits such as personality including empathy and hyperactivity. So twins, especially identical twins who share all of their genes, are more likely to have similar behavioral traits. Even growing up in different environments, the Jim twins followed life paths that were extremely similar. And while some may insist that nurture wins over nature, behavioral genetics argue that while some factors may appear to be environmental, they are largely reflections of genetic differences. 

The term nurture refers to the environment in which children grow up in. It poses the question, does the household children grow up in have more of an impact on their future than the genes their born with? Factors that fall under the environmental influences category are defining experiences, the roles and presence of family figures, where you live, how your parents treat you and what they teach you.  Even concepts picked up from the media surrounding a child can be influential. In the case of twins small nuances between the different types of twins can impact the identity of each person. An article from Guang Guo about the importance of twin studies says “ …identical twins are probably more often dressed alike than fraternal twins,” this, ”…makes identical twins more similar than fraternal twins, and we could mistakenly attribute effects to genes that are really due to differences in treatment.” The similarity in behavior seen in identical twins is due to the way people act and talk around them. Twins are relevant to this argument because they grow up in the same environment. The whole argument against the influence of nurture is that twins, fraternal or identical, grow up in the same environment. It’s like a control variable in a science experiment; you keep one condition the same, (in this case it’s the environment the kids grow up in ) and when the children develop differences genetics can be held responsible. However, this argument fails to consider the small things in environments that can have a big impact. Experiences we have as people are unique to ourselves and twins are their own separate people. There is no way to control the precise similarity in an environment in the real world. The way we are shaped is different for everyone, including twins. 

As twins ourselves, we have considered the environmental and genetic impacts in our own lives. We asked our twins what factors they found to be most influential. Ben Dorighi (Nina’s twin) says, “Definitely nurture because I feel like people are born with certain traits. But people’s personality and how they react to situations depends on how they’ve been raised and what ideas they’ve been shown.” For a boy girl twin pair, it is more likely that they will have more differences because the expectation that twins are the same is not as great. People don’t expect boy and girl twins to be similar which is why genetics play less of a role. Carly McClung, (Grace’s twin) agrees and says, “I think the environment is the most influential because, other than our looks, it influences our actions and thoughts.” For a same gender twin pair, it’s harder to be different because they are treated the same but more of an effort is made to be separate people. Even though genetics may influence our personality to some degree, our environment is more influential because it impacts our behavior. Overtime, this behavior makes us who we are. Also, our environment is always changing so who we are as people must change with it. While genetics do impact the majority of our physical traits, they don’t change so they have less opportunities to influence us.

While evidence can argue one or the other, in our opinion the nature vs nurture debate is too complicated to simplify. It can’t be narrowed down to just one category because there are so many other factors that influence a person’s traits and behavior. Instead, it is a combination of both. It is also hard to scientifically prove the extent of these influential factors because all people are different and it is difficult to control variables within a person’s life. This is why twins are appealing to researchers; they provide a window into a world of genetic studies and environmental impacts on human development.