Aliens: look at this species they've come up with this weird concept of "money". Some of them have more & can obtain more resources with it. Because they can't trust each other they need a book-keeping system that uses more resources than they needed in the first place! Quite ironic.
If you could provide a better solution, a Nobel Prize is waiting for you. It is truly extraordinary what people have achieved. Especially since around 18th century (wonder why..).
