It is silly to try to pinpoint if he hatched or was born if we dont even now what he is. Perhaps Yodas species were originally Midichlorians that evolved and produce asexually.
I always liked the theory that hes just this really old, crazy little human man. Like, a wizard of old or something. And I sure hope we never find out about his species' name and traits. That would suck.
Yoda (as i've said a few times) is what happens with excess Light Force usage, just like the Emperor is what happens with excess Dak Force usage. Luke always wonders why Yoda didn't just use all his power, which he already has, it was probably because he didn't want to get uglier!!
Yoda was just an inanimate piece of plastic, cloth and wire until a man named Frank Oz stuck his hand up his Jedi butt. It was the birth of a Jedi Master!
Its called Muppetmaking, and its usually brought to you by government sponsered PBS (so you know its good).