Twin Genetic Studies (Nature vs. Nurture)
Introduction
Over the years many scientific studies have been done on the genetics and behaviors of sets of twins that were separated at birth. The following three studies are all similar in purpose, tactics, and goals however they all clearly had very different findings. The studies were performed to find out which traits are biological (nature), and which ones are learned (nurture).
What scientists found, was that in many cases the subject s behavior was a result of a combination of both forces. By studying twins with the same genetic make-up that had lived apart all of their lives scientists were able to see more clearly the similarities and differences of the twins than if they had lived and been raised together.
In particular, some of the traits that the scientists tested were alcoholism, physical frailty of elderly black people, and obesity. The purpose of these studies were to figure out the differences in the twins, then find out which variable made one twin more or less likely to have their particular problem.
SUMMARY
The first study, The Genetics of Alcoholism , was in Alcohol Health and Research World in the summer of 1995. The research group, headed by Charles Kaij, started their study in Sweden where they found numerous sets of registered identical twins that had been adopted by different families. They then
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proceeded to track down and interview a sample of twins. Next they determined whether either of them showed signs of alcoholism. Previous research showed that 7.7 percent of the general public is classified as being alcoholic. However, if one of the twins was found to have the disease, then the other twin had a 28.3 percent chance of also being alcoholic. That works out to be a little more than one in four cases that have not just one, but both twins with alcoholism. This result shows that even though a large number of twins both had the disease, it was not guaranteed that the other one would have acquired it. Thus the scientists concluded that the risk of alcoholism greatly increases when one twin is found to have the disease, but it is not pre-determined by your genetic make-up.
The second study was called the Black Elderly Twin Study (BETS).
The goal of the study was to develop a twin sample for genetic studies of factors influencing the physical health of black Americans aged 65 years and older . BETS was published in 1995 in the Journal of Human Biology. A telephone survey was conducted in the spring of 1993, of 216 elderly black men and women that were twin pairs. The researchers asked a series of 23 questions, for example, Do you feel fatigued when showering or bathing yourself? The questions that they asked pertain to every person, male or female, young or old. Researchers found out that there is not a large correlation between twins and their physical state when older. To illustrate this, consider the population experience of hypertension, the most prevalent chronic disease of late life in the United States. Among persons aged 65-74 years in the United States, over 80.7% of blacks have Hypertension. The rate of Hypertension in the sets of twins was consistent with this fact, and twins were no more likely to have the disease than the average
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person. Researchers came to the conclusion that the lifestyle that the individual led was much more accurate in determining frailty at an elderly age than genetics were.
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The third and final study was done by a research group, headed by Robert Kohler in 1984, then later published in the Journal of Social Tendencies in March of1986. The study was done to find out what connection there was between the problem of obesity, and genetics. They wanted to see if the subjects were obese because of their environment, or if it was pre-determined by their genes. Obesity is defined as an individual that is thirty or more pounds over their recommended weight according to height. For example a six-foot tall man should weigh around 168 pounds. The researchers selected their subjects by digging into the Danish archive of twins. The Danish people have kept detailed records of twins, and they continued to follow up on them even as they got older, so this seemed to be a very logical place for the researchers to find information. They did surveys and conducted interviews with approximately 300 sets of twins varying in age from 20-67 years old, both male and female. The key difference in this study compared to all of the rest was that they surveyed both sets of twins that were raised apart, and sets that were raised together. The logic behind this was that they could get a better idea of which elements actually caused the person to be obese- their surroundings, or their genes. Their findings even surprised the researchers. What the statistics showed was that over 74.4 percent of the twins raised apart and 79.2 percent when the twins were raised together were both obese. They found very few sets of twins where only one individual was obese. The researchers concluded that since there were so many cases where both of the twins were obese, that it is almost guaranteed that that problem is genetic.
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Conclusion
The connection between all three studies it that although they had the same methodology and performed basically the same tests and surveys none of them have claimed to found the absolute answer of which traits are made by nature and which are formed by nurture. None of the studies produced complete, concrete evidence that the problem they were dealing with (alcoholism, frailty, or obesity) was unequivocally genetic or learned. As best stated by Kohler (1984) in regards to his study on obesity- These findings are statistically binding, yet still are not irrefutable Further scientific study would help solidify the researcher s findings. For example, a study on the relationship between adopted children, and their birth parents would help cement the facts and make them indisputable.
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Even though all of the research findings were different, one common goal was accomplished. Scientists gained a better understanding of how the body and mind work and which factors influence humans the most. These findings by researchers are not just beneficial to the twins themselves, but everyone could gain a better understanding of their behavior and body by examining these three studies.
