Where Genetics and Environment Meet in Monozygosity

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Where Genetics and Environment Meet in Monozygosity

According to the researchers from San Francisco State that human genetics don’t control for all outcomes by examining their health and fitness. / Photo by: ssilver via 123rf


A movie’s been newly made this year to depict the events of a scientific study that started in the 1960s, and it’s entitled Three Identical Strangers. The researchers split up triplets at birth to test out hypotheses about the age-old, nature-versus-nurture debate. As such, these triplets grew up apart from one another and found each other during their college days in the 1980s. They bore noticeably different personalities, and the film implies that it’s unknowable whether these differences were attributable to parents or not. With respect to fitness, the triplets all appeared to be the same, even wearing their hair the same way, and another study conducted more recently challenges the significance of so-called fitness genes.


The twin study focused on identical twins of age 52, but one was a triathlete while the other was a trucker. Researchers from San Francisco State determined that human genetics don’t control for all outcomes by examining this pair for their health and fitness. The subjects’ lives had been very different for the past 30 years, but they had been raised together in the same Midwestern U.S. household by the same parents. The triathlete ran 39,431 miles over 30 years and earned the All-World Bronze qualification for the ironman challenge in 2005. He now coaches a track team in high school. His brother stopped exercising many years ago and became a trucker, which brought with it a rather sedentary lifestyle.


The study reaffirms that the DNA of these twins, as is the case for monozygotic twins in general, is 99.9 percent the same, so for that incredibly minute, genetic disparity to coincide with such major differences in life choices and physical health, kinesiologist James Bagley came up with what he feels was the perfect way to study how a singular genome can react to these different lifestyles and environments and teach biologists about the ins and outs of heredity, adaptation, and environmental factors. “We had this opportunity to just cut out the genetic part totally, and just see what nurture does,” Bagley explains. “Any difference between them should be related to nutrition, where they live or exercise. So we brought them out here and did a battery of tests and the differences we found were some of the largest in the literature.”



This is actually in lockstep with a biological sciences trend that’s been playing out rather consistently as of late. Lots of researchers all over the world for the last few years have been focusing on circumstances that illustrate the idea that genes aren’t as deterministic as people tend to think. Many such studies have dealt with character traits like mental health qualities or behavioral tendencies—depression or aggression. They illustrate how environmental factors clearly have to be shaping these things to a greater extent than people typically surmise, but obviously, much more research is needed to figure out where nature ends and nurture picks up. In Bagley’s study, he even alluded to this saying, “They’re both super competitive, so we have to control for brother competitiveness.” Both share that characteristic, yet it clearly has manifested differently between them.


“It’s not a perfect copy machine,” according to behavioral geneticist Gene Fisch at Baruch College in New York. He’s talking about the aforementioned triplets but essentially addressing the same concepts that Bagley discussed with regard to monozygosity. A UPenn clinical psychologist, Rebecca Waller, furthers the point by saying that the phrase, nature versus nurture, is really a misnomer and that it’s better to refer to the debate as being more about genetics and environment—no “versus.” The two are cooperating after all. She gives points to epigenetics as the field that best embodies how to observe this because epigenetics is the phenomenon in which the environment controls how genes are expressed.


“You’re going to read more, and that’s going to make you even better,” Waller suggests. “And maybe because your parents see that, they buy you more books. Or maybe they drop you at the library on a Saturday.”  Researchers have basically been finding genes for some time now that correlate with upticks in one’s susceptibility toward depression, but there’s still no way to guarantee any particular outcome in that regard according to Patrick Sullivan, a genetics and psychiatry professor at the University of North Carolina, Chapel Hill. This is because of environmental factors having this so-far unquantifiable effect on how those genes are expressed.


Researchers have been finding genes for some time now that correlate with upticks in one’s susceptibility toward depression / Photo by: Сергей Дрозд via 123rf


“It depends what happens to you, what you’re taught, whether you learn skills about resilience, and the slings and arrows of outrageous fortune,” Sullivan says. The competitive twins were subjected to all kinds of exercises and even an arm wrestling challenge. The trained twin predictably outperformed the untrained one in all the physical fitness exams. He showed greater VO2 max, which is a metric for aerobic fitness important to runners and swimmers. He also exhibited lower cholesterol, lower blood pressure, and better health overall. What was more surprising, though, was that the untrained twin proved to have superior leg strength due to stronger muscles lining around his knees. Bagley hypothesized that this is because the untrained twin has been carrying more body weight than his trained brother for the past 30 years.


The experiments are actually ongoing. Though Bagley’s team already published on the subject, they intend to continue testing the twins for a broad miscellany of traits and their expressions. “We’re going to follow these guys up pretty much forever,” he says. “It’s a super rare situation, and they’re into it, too.”


The experiment between twins are hypothesized as the untrained twin has been carrying more body weight than his trained brother for the past 30 years. / Photo by: Ivonne Wierink via 123rf




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