The ancient Greek historian Herodotus recorded this account of the earliest language, a story old even in his day.
Herodotus, Histories, Book 2 chapter 2
Now before Psammetichus became pharoah of Egypt, the Egyptians believed that they were the oldest people on earth. But ever since Psammetichus became pharoah and wished to find out which people were the oldest, they have believed that the Phrygians were older than they, and they than everybody else.
Psammetichus, when he was in no way able to learn by inquiry which people had first come into being, devised a plan by which he took two newborn children of the common people and gave them to a shepherd to bring up among his flocks. He gave instructions that no one was to speak a word in their hearing; they were to stay by themselves in a lonely hut, and in due time the shepherd was to bring goats and give the children their milk and do everything else necessary.
Psammetichus did this, and gave these instructions, because he wanted to hear what speech would first come from the children, when they were past the age of indistinct babbling. And he had his wish; for one day, when the shepherd had done as he was told for two years, both children ran to him stretching out their hands and calling "Bekos!" as he opened the door and entered.
When he first heard this, he kept quiet about it; but when, coming often and paying careful attention, he kept hearing this same word, he told his master at last and brought the children into the king's presence as required. Psammetichus then heard them himself, and asked to what language the word "Bekos" belonged; he found it to be a Phrygian word, signifying bread.
Reasoning from this, the Egyptians acknowledged that the Phrygians were older than they. This is the story which I heard from the priests of Hephaestus' temple at Memphis; the Greeks say among many foolish things that Psammetichus had the children reared by women whose tongues he had cut out.