Chapter 1. From observing children in traditional upbringing to concepts of health -- Chapter 2. Human evolution, microorganisms, socioeconomic status and reconciling necessary microbial exposures with essential hygiene -- Chapter 3. Biodiversity, microbiomes, and human health -- Chapter 4. Regulation of host immunity by the gut microbiota -- Chapter 5. The gut microbiota and host metabolism -- Chapter 6. The impacts of the microbiota on animal development and physiology -- Chapter 7. The development of the gut microbiota in childhood, and its distortion by lifestyle changes -- Chapter 8. Distortion of the microbiota of the natural environment by human activities -- Chapter 9. The nature and functions of vertebrate skin microbiota -- Chapter 10. The influence of the microbiota on brain structure and function: Implications for stress-related neuropsychiatric disorders -- Chapter 11. Neurodegenerative diseases and the gut microbiota -- Chapter 12. Clinical application of the biodiversity hypothesis in the management of allergic disorders.

This edited collection of 12 chapters by research workers from a wide range of disciplines resolves the confusion that currently surrounds the "hygiene hypothesis" by considering the human need for exposure to microorganisms from an evolutionary point of view. The book explains why we evolved a requirement for exposure to microbiota from our mothers, from other people, and from the natural environment. It also explains the physiological roles of these exposures, what goes wrong when the exposures are distorted and how human lifestyles and activities, including degradation of the natural environment, are leading to this distortion. Particular attention is given to the range of pathologies associated with inappropriate microbial exposures and inappropriate colonization, including immunoregulatory problems such as allergies and autoimmunity, metabolic problems such as obesity and diabetes, and problems of central nervous system function and neurodegeneration. This book is of profound relevance to most medical disciplines, but also to those concerned with preserving the natural environment and with developing healthier urbanisation.