can you name a few of its categories or variations?
Australian Aboriginal sign languages  and Mofu-Gudur
Sign language
In non-signing communities, home sign is not a full language, but closer to a pidgin. Home sign is amorphous and generally idiosyncratic to a particular family, where a deaf child does not have contact with other deaf children and is not educated in sign. Such systems are not generally passed on from one generation to the next. Where they are passed on, creolization would be expected to occur, resulting in a full language. However, home sign may also be closer to full language in communities where the hearing population has a gestural mode of language; examples include various Australian Aboriginal sign languages and gestural systems across West Africa, such as Mofu-Gudur in Cameroon.
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 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
wiki:19674442
Sign language [SEP] Classification
Although sign languages have emerged naturally in deaf communities alongside or among spoken languages, they are unrelated to spoken languages and have different grammatical structures at their core. Sign languages may be classified by how they arise. In non-signing communities, home sign is not a full language, but closer to a pidgin. Home sign is amorphous and generally idiosyncratic to a particular family, where a deaf child does not have contact with other deaf children and is not educated in sign. Such systems are not generally passed on from one generation to the next. Where they are passed on, creolization would be expected to occur, resulting in a full language.