I've read that several bits of Japanese come from contractions with ある:
だcomes fromで + ある(source)なるcomes fromに + ある(source)たりcomes fromて + あり(source)たりcomes fromと + あり(source)- Adjective forms like
たのしかったcome from inflectingたのしく + ある(source)
Because contraction with ある seems to have occurred quite a few times, I started wondering if the suffix 〜がる (as in たがる or ほしがる) was a contraction of が + ある. I realize this is baseless speculation, but it sounded plausible to me, so I tried to look it up to see if it was right. Unfortunately, I couldn't find anything about the etymology of がる online, and my dictionaries don't say anything on the subject either.
Is this possible? Is there a better explanation?