The ability to voluntarily fold the lateral edges of the tongue upward into a tube or “taco” shape is a common physical trait. This simple action, known as tongue rolling, often sparks curiosity when an individual discovers they cannot perform the trick while others can. The inability involves a complex interplay of physical structure, muscle coordination, and genetics. Examining these biological factors helps explain why this seemingly effortless movement remains unattainable for some.
The Anatomy Required to Roll
Achieving the tubular shape of a tongue roll requires the precise and coordinated action of the organ’s muscle groups. The tongue is composed of eight paired muscles, divided into intrinsic muscles that change the tongue’s shape and extrinsic muscles that change its position. The primary driver for the rolling action is the superior longitudinal muscle, one of the intrinsic muscles.
This muscle runs along the upper surface of the tongue, and its contraction shortens the tongue and curls its edges upward. The simultaneous, controlled relaxation of other muscles, like the transverse and vertical intrinsic muscles, is necessary to shape the organ into a distinct tube. The styloglossus, an extrinsic muscle, may also assist by slightly elevating the lateral margins of the tongue.
Even with the correct neural command and muscle function, the physical dimensions of an individual’s tongue can mechanically prevent the action. Factors such as the size, thickness, and flexibility of the tongue body, and the length and attachment point of the lingual frenulum, impose anatomical limits. A particularly short or tight frenulum—the tissue connecting the underside of the tongue to the floor of the mouth—can restrict the necessary upward movement.
Dispelling the Genetic Myth
For decades, the inability to roll the tongue was mistakenly attributed to a simple lack of a single dominant gene, a concept known as Mendelian inheritance. This misconception originated with a 1940 paper by geneticist Alfred Sturtevant, who suggested the ability was determined by a single dominant trait. The notion became a common, yet scientifically flawed, example in biology classrooms.
The single-gene theory was formally disproven by studies involving identical twins, who share nearly all their genetic material. A 1952 study of 33 identical twin pairs found that approximately 21% were “discordant,” meaning one twin could roll their tongue while the other could not. If a single dominant gene solely controlled the trait, the concordance rate would be close to 100%.
The fact that two non-rolling parents can produce a child who can roll their tongue is further evidence that the trait is not a simple dominant/recessive switch. Scientists now understand that the ability is polygenic, meaning it is influenced by multiple genes that code for characteristics like muscle structure, motor control, and nerve development. While genetics play a role in predisposing a person to the ability, it is a complex influence rather than a simple, predetermined switch.
The Influence of Practice and Development
If the necessary anatomy is present and genetics provide a predisposition, the ability to roll the tongue often develops later in childhood. Studies of schoolchildren in Japan showed that the percentage of children who could roll their tongue increased significantly between the ages of six and twelve. This observation suggests that muscle control and coordination are still maturing during these years.
The capacity for motor learning and neuroplasticity suggests that the ability is not entirely fixed at birth. Research shows that a small percentage of individuals who initially cannot roll their tongue can acquire the skill through deliberate practice and focused effort. This successful learning demonstrates that the required neural pathways and fine motor control can be developed over time. Therefore, the inability to roll the tongue is typically a result of minor anatomical constraints or a lack of the motor development needed to master the complex, coordinated muscle movement.