Tongue rolling, the ability to curl the sides of the tongue upward into a tube, is a simple feat many can perform effortlessly. However, a notable portion of the population finds this action impossible. This disparity highlights the complex interplay of genetic predispositions and physical development.
The Interplay of Genetics and Environment
For many years, tongue rolling was widely taught as a simple Mendelian dominant genetic trait, determined by a single gene. This belief stemmed from a 1940 study by geneticist Alfred Sturtevant. However, this early conclusion has since been challenged. Modern scientific understanding reveals that tongue rolling is a complex trait, influenced by multiple genes.
Twin studies provide evidence against simple Mendelian inheritance, finding discordance in identical twins. A 1952 study of 33 identical twin pairs reported that 21% had one twin who could roll their tongue and one who could not. Since identical twins share nearly identical genetic material, such discrepancies indicate factors beyond a single gene. Furthermore, parents unable to roll their tongues sometimes have children who can, also contradicting the single-gene model.
Environmental factors, particularly practice and learning, also contribute to tongue rolling. Studies show some individuals who initially cannot perform the action can learn with conscious effort. Observations of Japanese schoolchildren revealed an increase in tongue-rolling prevalence from 54% in younger children to 76% by age 12, suggesting many learned the skill. This indicates that while genetic influences may create a predisposition, muscle control and coordination developed through experience also play a role.
Anatomical and Neurological Contributions
The physical ability to roll the tongue depends on the complex structure and function of its muscles. The tongue is composed of two main groups: intrinsic and extrinsic. Intrinsic muscles, including the superior and inferior longitudinal, transverse, and vertical muscles, originate and insert entirely within the tongue. These muscles change its shape, allowing it to shorten, lengthen, narrow, flatten, and curl, which forms the tube for rolling.
Extrinsic muscles, such as the genioglossus, hyoglossus, styloglossus, and palatoglossus, originate outside the tongue and insert into it. Their primary role is to move the tongue as a whole, facilitating actions like protrusion or retraction. While these muscles control the tongue’s position, the fine shaping for rolling relies heavily on the coordinated action of the intrinsic muscles. Individual variations in flexibility, strength, and structure of these muscle groups influence the capacity for tongue rolling.
The precise movements of the tongue are controlled by the nervous system. The hypoglossal nerve (twelfth cranial nerve) is a motor nerve that innervates nearly all intrinsic and extrinsic muscles of the tongue. It transmits signals from the brain to the tongue muscles. The brain’s ability to send precise, coordinated signals to these muscles is essential for complex tongue movements, including rolling.