Verified by Twins in Behavioral Science Research
The information gathered from the study of twins lays the groundwork for future genetic research, including the degree to which any aspects of life are determined by genetics, the location of specific genes, and the prevention and treatment of diseases and disorders. All of which makes them valuable to study.
Twins share everything from their in-utero environment and parents to birthdate and the classroom setting. One unusual case study involved two-and-a-half years old identical twins, one of whom nearly drowned in cold lake water. Researchers wondered whether he would suffer intellectual deficits. Later, the twins completed a number of tests that measured different skills. Surprisingly, meaningful cognitive differences between the two brothers were not found.
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What Twins Research Tells Us
There is much to celebrate in the research of twins. Even though many share environments before and after birth, no two twins are exactly the same. These conditions make every identical twin pair a mini-experiment. Close attention has been paid to identical twins reared apart by researchers such as Nancy Segal.
In 1875, Sir Francis Galton, a half-cousin of Charles Darwin, published research in the UK publication Fraser’s Magazine. His article, “The History of Twins, As a Criterion of the Relative Powers of Nature and Nurture,” describes the study of twins and how nature and nurture affect development.
Briana Mezuk and colleagues recruited some 50 pairs of identical twins from the Mid-Atlantic Twin Registry, the largest such registry in the US. The researchers found that studying twins can tell us how stress and mental health contribute to the risk of diseases like type-2 diabetes. And at King’s College London, the study of twins has focused on the genetics of healthy aging, examining the risk of diseases that include cardiovascular, metabolic, musculoskeletal, and ophthalmologic disorders.
In studies on mood, researchers have used inflammation indicators to help predict the severity of depressive symptoms. A study that examined twins, identicals who share 100 percent of their genes, found that the twin who registered a higher measure of inflammation was more likely to develop depression five years later.
This is a method in twin research that happens naturally, experimentally, or by chance when two identical twins have different experiences, and allows for a key comparison within the pair. Natural co-twin control happens when identical twin partners show differences in their appearance, health, or behavior that are not caused by any form of intervention. Experimental interventions occur when a researcher subjects one twin to a specific treatment or training program, and provides the other twin with a different experience or no treatment at all. For example, one twin may have been bullied, while the other was not, or one twin may have been exposed to the measles, while the other was not.
The Study of Twins
Throughout the years, many researchers have been examining twins. Twin registries are found throughout the world, all following thousands of identical and fraternal twins. Registries can be found in the United Kingdom, Norway, Sweden, and Finland, and the U.S. In this country alone, we have the National Academy of Sciences-National Research Council Twin Registry, the Minnesota Twin Registry, the Vietnam-Era Twin Registry, among many others.
Psychoanalyst Peter Newbauer directed the separation of four sets of identical twins and one set of identical triplets, as part of a longitudinal research project conducted in the 1960s and 1970s, which was funded by the NIMH. Newbauer was an NYU psychiatry professor who also consulted with a Jewish adoption agency; they arranged to have the newborn babies assigned to deliberately different adoptive parents--affluent versus non-affluent. This study was reported in various publications, as well as the documentary, Three Identical Strangers.
Astronaut Scott Kelly spent nearly a year in low-Earth orbit on the International Space Station in 2015-2016; meanwhile, his twin brother Mark, also an astronaut, stayed on Earth. Researchers wanted to see the effects of space travel in a genetically controlled situation. When compared with Mark, they found numerous changes in Scott such as bone density and altered telomeres—which protect the ends of chromosomes from the aging process. These changes, for the most part, returned to normal after his return to Earth.
The best-known research on twins reared apart was founded and run by psychologist Thomas Bouchard and his colleagues. The study has examined variance in traits—such as height, weight, IQ, rate of speech, and many other traits—in twins separated at birth and reared apart.
One of the world's largest twin research studies is The Swedish Twin Registry at the Karolinska Institute. It has data on 194,000 twins, including identicals and fraternals. The 60-year-old effort studies twins to help us understand health and disease including research on cancer, cognitive function, depression, substance use, ADHD, among many other areas. It has information on every twin born in Sweden since 1886.
This registry, founded in 1993, follows 12,000 twins, mostly made up of females and middle-aged or older. The registry has collected blood, urine, and tissue samples from identical and fraternal twins over the decades for comprehensive analysis of the biological makeup of twins.
In the early 20th century, the work of Josef Mengele as well as his mentor Otmar Freiherr von Verschuer included twins research. Mengele, known as the Angel of Death, conducted many experiments in Auschwitz during World War II. Both Mengele and von Verschuer used studies on twins to advance racial discrimination. Reportedly, Mengele sent specimens of eyes and blood samples from the 200 twins on which he conducted unethical human research, to von Verschuer for analysis. Only 10 percent of those twins survived Mengele's experimentation.
