I thiink, that if you go way back when we were cavmen etc, the need and drive to eat was the one thing that got us off our butts and find food. When we found it, then we'd eat as much as we possibly could as we didnt know when we would eat again.

That drive/instinct is still with us, but the scarcity or difficulties of finding food are not!

The ability to store fat that seems apparent in some and not others I think is a genetic thing that probably would have been an advantage in caveman times, it probably wouldnt have happened much or to the extent it does today though

Jo