I've had this assumption for a long time, just never posted it. I joined this forum today just because I wanted to talk about it. I noticed someone else, Raizen, has hit on this also, but i wanted to just put this out there. My assumption was that when you die, your devil's fruit goes back into the ocean for someone to find. When Roger died, everyone went around looking for it and Shanks was somehow able to come across it. This is when he met Luffy and when Luffy was able to get his current devil fruit power. It makes sense and seems to be around the same time, but they really haven't hinted at this anywhere that I have noticed in the manga. Any ideas? sources?