There are lots of traits we can blame solely on genetics, but as the Children’s Museum of Indianapolis explains, several studies over the last few decades have proved that belief wrong. Many of these studies involved identical twins. In some cases, one twin could roll their tongue while the other could not.
Even more interesting is the same 1951 study that looked at Japanese school children and the ratio of them that could roll their tongues. The University of Delaware states that while only 54% of children aged 6-7 could roll their tongues, 76% could roll their tongues by the age of 12. With other variables accounted for, the researchers concluded that the majority of the additional 22% had learned how to roll their tongues in the 5-6 years since they were last polled.
As Good Housekeeping puts it, people who want to roll their tongues may be able to learn the skill, regardless of their genetics. The skill itself is likely rooted in a mix of environmental and biological factors, leaving its single-source — if there is one — a mystery.