Paleo diets have been characterized as having foods that we “were born to eat,” and the justification for their healthful nature is based upon the assumption that they reflect the foods our Stone Age ancestors ate: low in sugar and cereals and high in meat and “healthy fats.” Here we critique this assumption by drawing on direct evidence of hominin diet from the bioarchaeological record (isotope and microfossil data) that shows that there was no such ubiquitous Stone Age diet. These data also demonstrate that plant foods, including cereals, were consumed by our ancestors many millennia before the Paleo diet proponents would have us believe and well before the agricultural revolution. We also probe our Eurocentric views of the genetic basis of metabolic syndrome-related diseases by reviewing the burden of these diseases, the possible skeletal evidence for this, from Oceania. This Oceanic case study underscores the diversity of our species, its histories, its ecologies, its genetics, and its diets. These differences extend over tens of thousands of years and demonstrate that there simply was not and is no signature one-size-fits-all diet from humankind’s past that is universally healthful.