Just another form of language....
"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?" Those were Socrates words, which is also one of the earliest written records of sign language from 5th century BC. Sign language was mainly created and developed for mute people, to express their thoughts and feeling to others. Just like English, Tamil or any other language, sign language was also developed natural