system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5 how the first ever language was created? What most probably was that language?
gpt
Short answer, nobody knows. 

Long answer five theories:

The Bow-Wow Theory
According to this theory, language began when our ancestors started imitating the natural sounds around them. The first speech was onomatopoeic--marked by echoic words such as moo, meow, splash, cuckoo, and bang.

What's wrong with this theory?
Relatively few words are onomatopoeic, and these words vary from one language to another. For instance, a dog's bark is heard as au au in Brazil, ham ham in Albania, and wang, wang in China. In addition, many onomatopoeic words are of recent origin, and not all are derived from natural sounds.

The Ding-Dong Theory
This theory, favored by Plato and Pythagoras, maintains that speech arose in response to the essential qualities of objects in the environment. The original sounds people made were supposedly in harmony with the world around them.

What's wrong with this theory?
Apart from some rare instances of sound symbolism, there's no persuasive evidence, in any language, of an innate connection between sound and meaning.

The La-La Theory
The Danish linguist Otto Jespersen suggested that language may have developed from sounds associated with love, play, and (especially) song.

What's wrong with this theory?
As David Crystal notes in How Language Works (Penguin, 2005), this theory still fails to account for "the gap between the emotional and the rational aspects of speech expression."

The Pooh-Pooh Theory
This theory holds that speech began with interjections--spontaneous cries of pain ("Ouch!"), surprise ("Oh!"), and other emotions ("Yabba dabba do!").

What's wrong with this theory?
No language contains very many interjections, and, Crystal points out, "the clicks, intakes of breath, and other noises which are used in this way bear little relationship to the vowels and consonants found in phonology."

The Yo-He-Ho Theory

According to this theory, language evolved from the grunts, groans, and snorts evoked by heavy physical labor.

What's wrong with this theory?
Though this notion may account for some of the rhythmic features of language, it doesn't go very far in explaining where words come from.