The Stone Age Diet: Based on in-depth studies of human ecology and the diet of man by Walter L. Voegtlin. This was self-published back in 1975. Only a couple hundred copies were printed and distributed to friends and relatives. No one knew the book existed until some years later. In no way is he the father of the paleo diet. It is impossible to purchase. Apparently his descendents are planning a reprint, though the book is poorly written and not based upon factual anthropological information that even was available then. We have put up his Functional and Structural Comparison of Man's Digestive Tract with that of a Dog and Sheep. And a PDF can be found here.
The rationale for the Paleolithic diet derives from proponents' claims relating to evolutionary medicine.:594 Advocates of the diet state that humans were genetically adapted to eating specifically those foods that were readily available to them in their local environments. These foods therefore shaped the nutritional needs of Paleolithic humans. They argue that the physiology and metabolism of modern humans have changed little since the Paleolithic era.:594–95 Natural selection is a long process, and the cultural and lifestyle changes introduced by western culture have occurred quickly. The argument is that modern humans have therefore not been able to adapt to the new circumstances. The agricultural revolution brought the addition of grains and dairy to the diet.
^ Hou JK, Lee D, Lewis J (October 2014). "Diet and inflammatory bowel disease: review of patient-targeted recommendations". Clinical Gastroenterology and Hepatology (Review). 12 (10): 1592–600. doi:10.1016/j.cgh.2013.09.063. PMC 4021001. PMID 24107394. Even less evidence exists for the efficacy of the SCD, FODMAP, or Paleo diets. Furthermore, the practicality of maintaining these interventions over long periods of time is doubtful.