Nature vs Nurture: What Can Twins Tell Us About This Ongoing Debate?

 

Have you ever wondered how much of your personality is inherited and how much is thanks to your environment? I sure have! The Nature vs Nurture debate has been an ongoing discussion since the year of 1869 when psychologist Sir Francis Galton, a cousin to Charles Darwin, coined the terms through numerous twin and family studies. To understand this continuously disputed concept, we first have to understand each term involved. Nature refers to our genetic composition and how this can affect everything from our hair color down to our ability to learn a new language. Nurture refers to the environmental variables such as culture, parenting, trauma, and childhood experiences and how each contributes to who we are as a person.

 

A major method to collect data for this debate are twin studies. Twin studies offer us an accurate way to judge how much of a disease, behavior, or tendency is due to our environment or whether it's our genetic makeup. Identical or monozygotic twins provide a way of determining the true environmental effect since both twins are genetically identical. If one twin has a trait that the other doesn't, researchers can conclude that that trait is due to environmental factors. The differences in monozygotic twins are due to something called epigenetic differences. Epigenetics is the study of how one's environment can affect whether a specific gene will be expressed. These traits/alterations are passed down to offspring through generations without ever changing the DNA sequence of an individual. 

 Variation in Traits due to Shared/Unshared Environments vs Genetics

Identical twins that are separated at birth give us a real insight into the influence of genetics when both grow up in different environments. A study from 1979 gives a great example of the impact of genetics on someone's habits. Jim Lewis and Jim Springer, twins separated at the age of 4 weeks old, were reunited when they were 39 years old to find that they were both nail biters, had usual tension-headaches, smoked the same type of cigarettes, drove the same car, and even vacationed on the same beach in Florida. Similarities like these show us how many surprising traits are actually encoded in your DNA and how your environment has less impact than you may think. Contributing to this idea, research conducted by the University of Minnesota on identical twins who grew up in different environments, shows that identical twins who were reared apart had the same chance of being psychologically and physiologically similar than those who grew up in the same environment. I.Q levels have been shown to also be mainly influenced by genetics and not environment. According to the same study done at the University of Minnesota, on average, only about 25% of your IQ level is by environmental influence while 75% is genetic. Although overruled by genetics, the 25% environmental part of your IQ conveys neuroplasticity. Neuroplasticity is the ability for a person's brain to change, modify and adapt through an individual's life. A study done in 2011 by University College London took a group of teenage boys and girls and measured their IQ levels as well as MRI images at the beginning of their teenage years (ages 12-15) and 4 years later (ages 16-20). The results of this study surprised many with increases and decreases of up to 20 points (equivalent to 20%) and visible changes in the grey matter regions of their brains. These results are clear evidence that IQ levels are not something completely determined by birth but can change throughout your teenage years pointing towards the fact that your environment plays a more influential role in intelligence/IQ levels then you may believe. This study also conveyed the message that there are ways we can improve our traits such as intelligence through changing/bettering our environment which may give hope to those who are not genetically fortunate. 

 
Although genetics clearly do play a huge role in someone's characteristics and personality, environment affects whether or not those genes are expressed. Imagine an on and off switch determined by where you live and grow up (your environment). Monozygotic twins have the same genes but different potentials to express them based on their environment. Perfect pitch, by example, is genetic but can only be expressed with early musical training. Susceptibility to mental illness is also something which is mainly affected by environment. In the documentary "Three Identical Strangers," which I highly recommend watching, three identical triplets are part of a study where they are separated at birth and reunited. While all three different home environments were in the same 100 mile radius, the main variable in the study was the socioeconomic environment as well as the presence of a father in the household. One boy grew up with a upperclass father who was a doctor and was often unavailable, one triplet received a working class father with whom he often clashed/fought with, and one grew up in a working class household with a loving, available father. This difference had a huge impact on the boys and their mental health: The triplet who clashed with his middle class father developed manic depression and eventually shot himself, the triplet with an unavailable father also became depressed later on in life, and the one with a loving father was able to cope with his depression unlike his identical siblings. This study shows that although genetics clearly have an impact on a variety of traits such as mental illness, the environment a child grows up in has a huge effect on how that gene may or may not be expressed.

    

These twin studies have driven researchers to come to the conclusion that the answer to the debate of "Nature vs Nurture" isn't "Nature" or "Nurture", instead, it's actually about the effect that the environment plays on the expression of specific genes within an individual. Although these studies provide valuable data about the effect of the environment on an individual's behavior and personality, I feel the need to include that although important, these twin studies have also been very unethical. Many of these twins and triplets didn't even know that they were separated or were being studied! Maybe the real question is: Were the results of these studies significant enough to separate babies at birth without consent? I did some research into this bioethical question and didn't find much information as to whether or not studies as such are still going on. Twin studies are still occurring, but, from what I have found, they're voluntary and by sign-up!