Similar or Different?
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Media often presents twins, especially those separated at birth, in the most sensational manner which clouds the view of the public and researchers with the myth that identical twins are near-perfect copies down to the habits and preferences. This myth has grown in popular culture and gives rise to much erroneous thought, such as traits solely determined by genetics. Twins are not identical copies and to discount environmental influencers is to ignore a very large part of what constitutes a person.
The Importance of Twin Studies
Twin studies provide insight into how genes and environment influence human behavior and health. By comparing the similarities and differences between identical twins (who share 100% of their genes) and fraternal twins (who share 50% of their genes), researchers can estimate the relative contributions of nature and nurture to various traits and outcomes. Twin studies have been used to investigate a wide range of topics in psychology, such as autism, schizophrenia, depression, intelligence, personality, aging, and substance abuse.
However, these studies can be misleading when cited for genetic purposes, as they may imply that people have predetermined traits and dispositions based on their similarities. However, genetics are not the sole factor that determines mentality and attitudes. Genetics and hereditary predispositions account for some of the development of an individual’s characteristics; for instance, temperament can be influenced by genetic dispositions. Nevertheless, the environments in which a child is nurtured are diverse and complex. These environments have multiple layers of forces that range from family and friends to school systems and governments. The multiple layers of environmental factors also affect temperament. These social and cultural factors play a significant role in psychological development, and twin studies show both similarities and wide-ranging differences among individuals with similar genetics.
The Benefits of Twin Studies
Twin studies are often misleading because there are many benefits derived from individuals who share genetics. Perhaps most vital to genetic research is the natural experiment twins provide that controls genetic confounding. Unlike other research designs that rely on artificial manipulation or matching of variables, twin studies take advantage of the natural variation in genetic relatedness among twins. This allows researchers to isolate the effects of environmental factors on behavior and health, without worrying about genetic differences that might bias the results.
For example, suppose researchers want to study the effects of parental divorce on children’s academic performance. They could compare the test scores of twins who were raised by divorced parents with those of twins who were raised by married parents. If the twins are identical (monozygotic), they share 100% of their genes. If the twins are fraternal (dizygotic), they share 50% of their genes. By comparing the test scores of identical and fraternal twins, the researchers can estimate how much of the variation in academic performance is due to genetic factors and how much is due to environmental factors. If identical twins show more similarity in test scores than fraternal twins, this suggests that genes play a bigger role than environment. If identical and fraternal twins show similar levels of similarity in test scores, this suggests that environment plays a bigger role than genes. This way, the researchers can isolate the effects of parental divorce on academic performance, without worrying about genetic differences that might bias the results.
Twin studies also reveal the importance of both genes and environment. Twin studies have shown that almost every trait and outcome is influenced by both genetic and environmental factors, to varying degrees. For example, twin studies found autism is highly heritable (about 60% of the variation in autistic behaviors is due to genetic factors), but also influenced by environmental factors (about 40% of identical twins do not share the same autism diagnosis) . Similarly, twin studies have found that intelligence is moderately heritable (about 50% of the variation in IQ scores is due to genetic factors), but also influenced by environmental factors such as education, nutrition, and stimulation.
They inform prevention and treatment strategies. Twin studies can help identify risk factors and protective factors for various diseases and disorders, as well as potential interventions that can modify these factors. For example, twin studies found stress and mental health problems can increase the risk of type-2 diabetes, suggesting that psychological interventions might help prevent or manage this condition . Twin studies have also found that genetic factors influence the response to different types of treatments, such as antidepressants or cognitive-behavioral therapy, suggesting that personalized medicine might improve outcomes for patients.
Of course, twin studies are not without limitations.
The Drawbacks of Twin Studies
One of the major drawbacks to twin studies is the reliance on assumptions that may not always hold true. Sometimes, twin studies assume identical twins and fraternal twins are equally similar in their environments, and that there are no interactions or correlations between genes and environment. However, these assumptions may be violated in some cases. For example, identical twins may experience more similar environments than fraternal twins, because they look more alike or have more shared interests. Alternatively, genes may influence the environment, or vice versa, creating a feedback loop that confounds the estimates of genetic and environmental effects.
Twin studies also require large and representative samples of twins. Twin studies need to recruit enough pairs of twins to have sufficient statistical power to detect meaningful effects. This can be challenging, especially for rare traits or outcomes. Moreover, twin studies need to ensure that their samples are representative of the general population, or at least account for potential biases due to selection or attrition. For example, some twin registries may over-represent certain ethnic groups or socioeconomic statuses, which could affect the generalizability of the findings.
Perhaps most important is the inability of twin studies to pinpoint specific genes or environmental factors. Twin studies provide an overall estimate of how much variation in a trait or outcome is due to genetic or environmental factors, but they cannot identify which genes or environmental factors are responsible for these effects. To do so, researchers need to use other methods, such as genome-wide association studies or randomized controlled trials, which can pinpoint specific causal factors and mechanisms.
Sensationalism's Impact on Twin Studies
The study of identical twins provides a large benefit in that researchers can study the influence of genetics on behavior and mental health
In conclusion, twin studies are a valuable source of information for psychology and related fields. They offer a unique opportunity to disentangle the complex interplay between genes and environment in shaping human behavior and health. However, they also have some limitations that need to be acknowledged and addressed. Twin studies should be seen as one piece of the puzzle, rather than the whole picture.
According to Thomas Bouchard “On average, identical twins raised separately are about fifty percent similar — and that defeats the widespread belief that identical twins are carbon copies” (Allen, 1998). This dictates that social influence has a profound impact on development. There may also be issues with studying twins having to do with research bias. There media sensationalizes the oddness of similarities, which overlooks the reality of the research:
When journalists first began interviewing Bouchard’s twins-raised-apart, they focused on the spectacularly similar pairs, like the Springer-Lewis twins. But those twins turned out to be outliers in the Minnesota study. Most of the other twins weren’t nearly as alike.
Media tends to overstate the similarities between twins most likely due to the sensationalism of stories such as twins separated at birth who turn out to be similar in many aspects of their lives. These stories are abundant but they are anomalies. Researchers need to be careful not to look for similarities in this way or they may bias their results. As a society we need to also look beyond the headlines because viewing people as carbon copies can lead to stereotyping groups based on genetic dispositions. If you believe that genetics dictate behavior without influence, then racial groups become prone to social taxonomy, which often becomes erroneous justification for prejudices.
Despite these drawbacks, twin research does offer an intriguing view into the manner in which genetics and environment mesh and develop an individual.
Photo by Gustavo Lanes
