Dietary fibre is the most important factor that modulates human biology &speciation. A low intake of dietary fibre with a diet rich in protein &fat leads to increased endosymbiotic and colonic archaeal growth and neanderthalisation of the species. This leads to induction of the Warburg phenotype &increased incidence of metabolic syndrome x, neurodegeneration, autoimmune disease, cancer, schizophrenia and autism. A population consuming a low fibre diet rich in protein and fat has its digestion happening in the small intestine. The population with predominant low fibre diet and small intestine digestion has got an increased predilection for civilizational disease. A high intake of dietary fibre leads to predominant large intestinal digestion by colonic microflora &inhibits endosymbiotic and colonic archaeal growth producing homo sapienisation of the species. This leads to decreased archaeal growth and incidence of civilizational disease. Civilizational diseases like autoimmune disease, metabolic syndrome, cancer, schizophrenia, autism &neurodegeneration can be controlled by a high fibre diet, inhibiting archaeal growth &endosymbiosis and by promotion of large intestinal digestion.