Now this is just the situation as regards primitive peoples. Their history _has_ been wiped out—it was never preserved by themselves or their neighbors. But knowledge of the geographical occurrence of a custom or invention, usually affords rather reliable insight into its history, sometimes into its origin. When the available information shows that Indian corn was grown by all the tribes from Chile and Brazil to Arizona and Quebec, it is evident that the history of native American agriculture is as much of a unit, essentially, as the history of Christianity or of fire-arms. It is a story of _invention_ only at its outset, of _diffusion_ and amplification through its greater length. When pottery is further discovered to possess almost exactly the same aboriginal distribution as maize, it becomes likely that this art, too, was devised but once; and likely, further, that it was invented at about the same time as maize culture and diffused with it.