Whether seen as a blessing or a curse, twins are a truly fascinating part of nature. It's estimated that there are around 110,000 sets of twins born every year in the USA, showing that two heads are sometimes better than one.
Scientists are obsessed with finding out how twins are formed in the womb and how close they remain while out in the wide world.
Everything from sun exposure to their diets is picked apart as researchers demand to know more.
Mary-Kate and Ashley Olsen, Dylan and Cole Sprouse, and Tia and Tamera Mowry are just some of the twins who've made names for themselves thanks to this unique bond, but what about the general public?
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Although there are skeptics, some twins even claim they have telepathy with each other.
That might not be as far-fetched as you'd think, as studies starting in 1979 looked at twins who were raised separately and brought up some fascinating results.
Conducted at the University of Minnesota by Thomas J. Bouchard Jr., studies honed in on monozygotic (identical) twins who were separated at or near birth and then raised in separate homes.
Analyzing psychological, physiological, and behavioral traits, 100 sets of twins and even triplets were monitored over the years.
The key factors included the idea that twins who were raised apart were spookily similar to those raised together. One source noted that the concordance rate (probability that twins share a trait or disorder) was 86% among identical twins raised together, 76% in identical twins raised apart, 55% in fraternal twins raised together, and 47% in siblings raised together.
Discussing the findings, the Minnesotans wrote: "The effect of being reared in the same home is negligible for many psychological traits.
"We infer that the diverse cultural agents of our society, in particular most parents, are less effective in imprinting their distinctive stamp on the children developing within their spheres of influence—or are less inclined to do so—than has been supposed.”
Importantly, the Minnesota twin study became one of the most referenced investigations in the field of behavioral genetics.
It's not without its critics, with some claiming that adoption agencies might've placed twins in similar homes and unintentionally skewed results.
There have been calls for further studies, but fundamentally, many agree that the Minnesota Study of Twins Reared Apart emphasizes the importance of personal experiences.
It's also caught the attention of Nancy L. Segal, a professor of developmental psychology and the director of the Twin Studies Center at California State University, Fullerton. Segal has dedicated her life to the study of twins, writing the likes of 2011's Someone Else's Twin: The True Story of Babies Switched at Birth and 2012's Born Together-Reared Apart: The Landmark Minnesota Twin Study. As said by Bouchard Jr. and appearing at the end of Segal's Born Together-Reared Apart, twins are still unique: "Twin studies refute both biological and environmental determinism. They do not negate the effect of the environment on behavior, nor do they over glorify the role of genes. They account for the uniqueness of each of us."