Yes, that's me, acting like a goofball.

I learned something neat the other day.

Think back to your high school biology class.  When you were studying genetics, your teacher probably told you that being able to roll your tongue is a dominant trait and not being able to roll it is recessive.  That’s not actually true.

There are pairs of identical twins out there where one twin can roll their tongue and the other can’t.

That by itself doesn’t mean that tongue-rolling isn’t genetic.  There are traits out there that are controlled partly by genes and partly by factors we don’t fully understand.  Schizophrenia, for example, is partly genetic.  Yet there are pairs of identical twins out there where one twin gets the disease and the other doesn’t.  Something about the environment triggers the disease in only one of the twins.

You’d expect, though, that if genetics has something to do with tongue rolling, then identical twins should be more likely to both be able (or unable) to roll their tongue than any other two people.  Scientists from the University of Adelaide in South Australia actually tested this way back in 1975.*  They surveyed 47 pairs of twins, some of whom were identical, about their ability to roll their tongue.  The result: the identical twins weren’t any more likely to both be able to roll their tongue than the fraternal twins.  The study didn’t find that genetics had anything to do with tongue rolling.

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*  If you want to read the study, look here: Martin, N.G.  No evidence for a genetic basis of tongue rolling or hand clasping.  J Hered (1975) 66(3): 179-180.