Unfortunately, the identification of the trait had been published already in textbooks and genetics books at the time he expressed his doubts. He stated these reservations in a later publication but no one seemed to pay attention to his retraction. But I am still embarrassed to see it listed in some current works as established Mendelian case. The difference in results for tongue rolling between each pair of twins was similar. The discordance in identical twins was similar to the discordance in fraternal twins.
Tongue rolling is a trait that can be learned and lacks definitive evidence.
It is not an example of simple Mendelian inheritance. It is for these reasons that I have discontinued using it as part of my genetics program in my classes and on the Internet. His explanation of the history of this trait leads to serious discussion of the non-genetic problems it raises. Several questions are listed here in case they need an illustration. Thank you for your interest and cooperation in this project.