Linguists debate whether all languages are descended from a common ancestor. This can’t be completely true, since many sign languages have been invented out of whole cloth in modern time (Nicaraguan sign is a famous example), as was, to a meaningful extent, Hawaiian Pidgin.
However, students of history know from the ancient Greek historian Herodotus that Phrygian is the first language. According to his writings, an Egyptian king by the name of Psammetichus ordered that two children “of the ordinary sort” be raised in an isolated cabin without exposure to language. At the age of two or so, the children began to speak Phrygian, which was taken as proof that Phrygian, not Egyptian, is the world’s earliest language.
This study is a great example of why experiments need to be replicated before they are taken too seriously.