Well based off what I can tell original alchemy originated as an experimental science of trying to turn other elements into gold(which failed and has yet to be done). And as time advanced alchemy became something more; it became the idea of a science that allowed you to change any one thing into another as long as the mass in trade was equivalent (equivalent exchange prinicple). So as you can see alchemy in "Fullmetal Alchemist" may be exagerated a bit but it sticks to the core ideas.