Deloria attempts to expose what he thought were fundamental weaknesses in this theory by detailing supposed archeological inconsistencies and positing alternative hypotheses that he believed align better with his understanding of the origins of Native Americans.

In a similar vein, he criticized the so-called "overkill hypothesis", which proposes that humans migrating into the Americas were partially responsible, by overhunting, for the sudden and rapid extinction of North American megafauna during the Pleistocene epoch.

Deloria believed that this hypothesis was racist; he contended that the Pleistocene extinction had no parallel on such a scale in Eurasia, which also experienced the sudden arrival of human hunters.

Despite admitting a wish that the book "had been more attentive to evidence, historiography, interpretation and argument," he notes that it did reveal problems with "supposedly neutral science-based narratives of the deep past," many of which have since been revised or replaced altogether.

Vine Deloria, he suggests, wanted those writing about the deep past to stop "universalizing their own epistemic position" and to accept that Indigenous histories might have something to teach them.