From the article: "Fitch’s experiments were inconclusive on the subject of whether Chomsky’s universal grammar applied to the Pirahã" And Tecumseh Fitch is the

From the article: "Fitch’s experiments were inconclusive on the subject of whether Chomsky’s universal grammar applied to the Pirahã" And Tecumseh Fitch is the one who developed a concept of Recursion in linguistics. How do you explain that?