For anyone who can still proudly recall one factoid learned in high school biology—that the ability to roll one's tongue is genetic—bad news: You learned it wrong. John McDonald, an evolutionary biologist, is out to debunk what he calls a myth about the genetic roots of tongue-rolling, PBS News reports. He says many of his undergrad students walk into class at the University of Delaware believing the skill is passed down through generations, and you can see why in textbooks like Biology for CXC: "Try rolling your tongue longways into a U-shape," the book reads. "Some people can do this, others can't. Tongue-rolling is caused by a dominant gene which we can call T." Pretty specific, yet untrue, says McDonald. The misinformation began in 1940, when geneticist Alfred Sturtevant wrote that tongue rolling was a genetic trait that relies on one dominant gene.
His theory was debunked 12 years later by researcher Philip Matlock, who noted that in seven of 33 pairs of identical twins, one twin could roll his tongue while the other couldn't. (His 1952 paper also noted 65% of the population has a tongue-rolling ability.) That ruled out the dominant gene theory, and Sturtevant later backed down. Yet the belief remains so dominant that McDonald says kids have written him fearing they were adopted because they can't tongue-roll like their parents. Genetics may play some role, however. McDonald points to a 1971 study that found non-identical twins were twice as likely to not share tongue-rolling ability as identical ones, "which is additional evidence that there is some genetic influence." Still, "tongue rolling is not a simple genetic character," he writes at the University of Delaware. "Despite this, tongue rolling is probably the most commonly used classroom example of a simple genetic trait in humans." (Speaking of genetics, you and your spouse may have similar DNA.)