A single dominant gene controls the ability to learn grammar, said a researcher who studied a family whose members don't know to add "ed" for the past tense of verbs or "s" for plural nouns.
Myrna Gopnik of Montreal's McGill University said Monday that studies show that in all other ways the members are intellectually normal.
But, she said, "Language is a problem they solve by sheer wit."
She said people lacking the grammar gene "are worn out just by talking" because they must continually struggle with verb tense and noun plurals.
"The hardest part for them is people thinking that they are stupid," Gopnik said. "They are not. You have to think of them as people without a native language."
Gopnik reported on her research at the meeting of the American Association for the Advancement of Science.
Steven Pinker of the Massachusetts Institute of Technology said that it was first suggested in the 1960s that there was a genetic component to learning language and that recent studies, such as that by Gopnik, support that belief.
He said his research shows that learning words and learning to apply the rules of grammar are two different functions springing from different parts of the brain.
People with a normal grammar gene naturally learn language rules that make verbs past tense or turn nouns into plurals, Gopnik said.
People lacking the gene, however, must learn through another intellectual process how to change verbs and nouns.
"They will say, "today I walk, yesterday I .
.' and they don't know how to finish," said Gopnik. "For some reason they don't build the general rules of language" such as adding the "ed" to make walk past tense.
Gopnik studied a family in which, of 30 members across three generations, 16 suffered from the inability to learn grammar rules. Otherwise, the 16 were normal, as were the unaffected family members.
Inheriting the language defect follows classic rules of genetics, said Gopnik. A member of the family has a 30 percent chance of inheriting the language problem, while the rest of the population has a 3 percent chance.
Studies by other researchers have supported the existence of a grammar gene, she said.
One showed that if one identical twin suffered a language difficulty, there was an 80 percent chance the other would also, said Gopnik. For non-identical twins, there was only a 35 percent chance both would have the problem.
Thomas G. Bever of the University of Rochester said his research shows that families with left-handed members may inherit a tendency to process language differently.
He said right-handers with no left-handed family members are more sensitive to the grammatical structures of language than are right-handers with left-handed relatives.
Right-handers with some left-handed relatives can recall and use individual words more skillfully than members of an all right-handed family, said Bever.
This suggests, he said, that there is an inherited or genetic component to naturally learning grammar rules or in the ability to use individual words.