After 1839, this worldview, the notion that the Americas had always been a land occupied by primitive, inferior people, would change forever. And so would the assumption that writing, mathematics, astronomy, art, monumental architecture—civilization itself—was only possible through so-called "diffusion" from within one part of the "Old World" to another, and from the civilized "Old World" to the uncivilized "New." Stephens and Catherwood's historic journey radically altered our understanding of human evolution. In their wake, it became possible to comprehend civilization as an inherent trait of human cultural progress, perhaps coded into our genes; a characteristic that allows advanced societies to grow out of primitive ones, organically, separately, and without contact, as occurred in Central America and the Western Hemisphere, which were isolated from the rest of the world for more than fifteen thousand years. And, just as with the Old World's ancient civilizations, they can collapse, too, leaving behind only remnants of their previous splendor.