Here's a Coach bag that looks similar to the Birkin. Oh, and by the way, this Coach bag is pretty new:
Designers seem to copy the shape and style of the bag a lot but not every detail. Versace seems to copy the Le Fabuleux and Speedy shapes from LV, but not to the point where they'll get sued.
The Birkin came from Hermes Haut a Courroies. I don't know when the HAC came about, but I think it's been around for a while.
I read somewhere on tPF (don't remember where) that the top of the LV Steamer actually was the inspiration for the Birkin...