although i'm not exactly sure what "ska" is these days... seems like people are labelling it as anything from older, reggae influenced, "madness" style stuff to what is basically punk or emo ("emotional" punk) with a few horns thrown in...
Ska orignally came from jamaica and came from jamica R&B. It funny when you listen to original early ska there is very little use of lyrics. Go listen to a group like the skalites who are probaly one of the best known of all the early ska groups and they sound northing like what most people think is ska now.
The main group to bring ska, dub and dancehall into the main stream music are the clash, with the albums the clash londons calling and sandadista. Alot of what people call ska is becasue of what they did even though what they did was not ska. What they did was closer to dub, reggae and dance hall, esp working with the likes of mikey dread and don letts.