Twins have always fascinated scientists, especially as the subjects of studies about the influence of environment and genetics.
The new documentary “Three Identical Strangers,” which is now in theaters, tells the story of the ultimate test of nature versus nurture: it follows three identical brothers who were separated at birth and raised by different families.
In 1980, two of the brothers met while attending Sullivan County Community College, and after making headlines, found the third triplet. Aside from looking alike, the three shared similar behavioral quirks and preferences.
But they were not the only twins in the study — according to NPR, of the 13 children involved, three sets of twins and one set of triplets have discovered one another. A book titled “Identical Strangers: A Memoir of Twins Separated and Reunited” was published in 2007 by a pair of twins who were also involved, Elyse Schein and Paula Bernstein.
The other four subjects still do not know they have identical twins.
The study was conducted by child psychiatrist Peter Neubauer and Violet Bernard, a child psychologist. They worked with the Louise Wise Agency, which matched Jewish orphans with adoptive families, to craft a secret experiment that would test how much of a person’s behavior is genetically influenced and how much is environmentally influenced.
The researchers carefully controlled which families the identical siblings ended up in, withheld information about their biological parents, and didn’t tell the adoptive families that the children were twins or had siblings. Instead, they told the families that their children were being followed for a study about the development of adopted children.
The study ultimately ended in 1980, and because of the fear of backlash and controversy over ethics and consent, Neubauer never published the results. The data is sealed in a Yale archive until 2066.
This is the only twin study that followed its subjects from infancy, but it’s far from the only time scientists have used genetically identical siblings in research.
Conducted properly, twin experiments can give scientists insights into how different habits, treatments, or lifestyles affect two people with the same genetic makeup. Studying identical twins can also help scientists pinpoint the effect of epigenetics, or environmental influences, on gene expression and function. This can help determine if certain traits or diseases lean more heavily on genetics or the environment.
In history, twins have been used in research about I.Q., everyday diseases, eating disorders, obesity, developmental and psychological traits, and sexual orientation, according to Smithsonian Magazine.
In a comprehensive review of twin studies worldwide, which was published in Nature Genetics in 2015, researchers found that on average, environment and genetics have a 50/50 influence on a person’s traits and disease. But certain conditions like bipolar disorder rely more heavily on genetics.
Today, twin studies are still commonly used. There are studies on mood and anxiety disorders as well as asthma and allergies. The Minnesota Center for Twin and Family Research collects community-contributed data from twins that helps them map out mental health outcomes and examine the development of substance use and related behavior disorders. For one study, they examined personality development of twins to see whether environment or genes played a role in risk-taking behaviors that lead to substance abuse.
Most famous, however, are NASA’s twin studies. After astronaut Scott Kelly got back from a year in space, scientists observed that 7% of his genes were expressed differently than those of his identical twin. The genes that were altered were related to the immune system, bone formation, DNA repair, and responses to an oxygen-depleted or carbon-dioxide rich environment.
On top of this, Scott Kelly’s telomeres — the caps at the ends of our chromosomes that affects cell aging — appeared to get longer in space, but they shrunk back when he returned to Earth. His gut also hosted different bacteria, and he returned two inches taller.
NASA recently sent 20 mice into space while their twins stay on Earth. In partnership with astronauts on the International Space Station, agency scientists plan to study changes in the rodents’ microbiomes and circadian cycles.