what is the earliest recorded evidence of the use of this language?
From  fifth century BC, in Plato's "Cratylus", where Socrates says: "If we hadn't a voice or a tongue, and wanted to express things to one another, wouldn't we try to make signs by moving our hands, head, and the rest of our body, just as dumb people do at present
Sign language
Groups of deaf people have used sign languages throughout history. One of the earliest written records of a sign language is from the fifth century BC, in Plato's "Cratylus", where Socrates says: "If we hadn't a voice or a tongue, and wanted to express things to one another, wouldn't we try to make signs by moving our hands, head, and the rest of our body, just as dumb people do at present?"

when does vocabulary develop slowly and when does it develop quickly It develops slowly around the age of one year and develop quickly around 18 months how can languages be expressed, other than through speech? Through sign language
wiki:19674426
Sign language [SEP] History
Pedro Ponce de León (1520–1584) is said to have developed the first manual alphabet. In 1620, Juan Pablo Bonet published (‘Reduction of letters and art for teaching mute people to speak') in Madrid. It is considered the first modern treatise of sign language phonetics, setting out a method of oral education for deaf people and a manual alphabet. In Britain, manual alphabets were also in use for a number of purposes, such as secret communication, public speaking, or communication by deaf people. In 1648, John Bulwer described "Master Babington", a deaf man proficient in the use of a manual alphabet, "contryved on the joynts of his fingers", whose wife could converse with him easily, even in the dark through the use of tactile signing.