I've always thought of the Forest Giants and the Trow as sort of "brother" creatures.
They are the same size, but completely opposite in every behavioral way. Forest Giants are into growth and gradual death, whereas Trow are builders and destroyers. They both worship mysterious gods, they've both been around since before the world was, really. But most of all, they both turn to stone when they are about to die. Now, that's a strange characteristic for one creature to have, but for TWO creatures to share this seems like too great a coincidence. I believe that the Forest Giants and the Trow were once one species, but their hate for one another has changed them.
Weird theory. It's been awhile since I've seen any weird theories on here, so I thought this thread was the perfect opportunity.