Rolling your tongue is not a genetic trait. Most of the people reading this were told, at some point during their schooling, that it was. At last you can read the paper that started the myth, and find out how quickly it was disproved.
Some of us had our tiny egos crushed in the third grade when a teacher, during a science presentation, tried to explain genetics by having the entire classroom roll their tongues. When some people couldn't, the teacher announced that the ability to roll one's tongue was genetic. The flat-tongued among us would never be able to twist their tongues into a roll, and should just give up. The inspiration from that lesson came from "A New Inherited Character in Man," published in 1940.
By 1952, the substance of the paper was discredited, although the authors of the paper did a decent job in rounding up 280 subjects, 65% of which were able to curl their tongues. After analyzing the family history of tongue curlers and non-tongue curlers alike, the researchers believed that the ability was at least in part the product of genetics. Mothers and fathers had equal influence on their offspring's ability to curl their tongues, and the sets of identical twins that the researchers studied both had the same ability to curl their tongues. The fact that genetics determined tongue dexterity (linguarity?), caught the popular imagination, and held up scientifically... for 12 years.
In 1952, the first cracks started appearing in the genetic tongue curling theory. For one thing, another study concluded that sets of identical twins sometimes did have differing abilities to curl their tongues. Out of 33 sets of twins, seven sets included both a roller and a non-roller. As they had exactly the same DNA, the theory couldn't be what it was cracked up to be. Another study was even more damning. When first approached by scientists, certain children were not able to roll their tongues. A few years later, the scientists paid them another call, and the kids were easily able to roll their tongues.
And yet the myth persists. In the end, it's a better story than it is a theory. Or perhaps, as we see from the enduring myth of the tongue map, theories about tongues tend to linger.
Image: Gideon Tsang.