to these microorganisms. "Microorganisms and macroorganisms such as helminths from mud, animals, and feces play a critical role in driving immunoregulation" (Rook, 2012). Essential microorganisms play a crucial role in building and training immune functions that fight off and repel some diseases, and protect against excessive inflammation, which has been implicated in several diseases. For instance, recent studies have found evidence supporting inflammation as a contributing factor in Alzheimer's Disease. Specific explanations This is a partial list: all links here go to a section describing or debating its evolutionary origin. Life stage related Adipose tissue in human infants Arthritis and other chronic inflammatory diseases Ageing Alzheimer disease Childhood Menarche Menopause Menstruation Morning sickness Other Atherosclerosis Arthritis and other chronic inflammatory diseases Cough] Cystic fibrosis Dental occlusion Diabetes Type II Diarrhea Essential hypertension Fever Gestational hypertension Gout Iron deficiency (paradoxical benefits) Obesity Phenylketonuria Placebos Osteoporosis Red blood cell polymorphism disorders Sickle cell anemia Sickness behavior Women's reproductive cancers Evolutionary psychology As noted in the table below, adaptationist hypotheses regarding the etiology of psychological disorders are often based on analogies with evolutionary perspectives on medicine and physiological dysfunctions (see in particular, Randy Nesse and George C. Williams' book Why We Get Sick). Evolutionary psychiatrists and psychologists suggest that some mental disorders likely have multiple causes. See several topic areas, and the associated references, below. Agoraphobia Anxiety Depression Drug abuse Schizophrenia Unhappiness History Charles Darwin did not discuss the implications of his work for medicine, though biologists quickly appreciated the germ theory of disease and its implications for understanding the evolution of pathogens, as well as an organism's need to defend against them. Medicine, in turn, ignored evolution, and instead focused (as done in the hard sciences) upon proximate mechanical causes. George C. Williams was the first to apply evolutionary theory to health in the context of senescence. Also in the 1950s, John Bowlby approached the problem of disturbed child development from an evolutionary perspective upon attachment. An important theoretical development was Nikolaas Tinbergen's distinction made originally in ethology between evolutionary and proximate mechanisms. Randolph M. Nesse summarizes its relevance to medicine: The paper of Paul Ewald in 1980, "Evolutionary Biology and the Treatment of Signs and Symptoms of Infectious Disease", and that of Williams and Nesse in 1991, "The Dawn of Darwinian Medicine" were key developments. The latter paper "draw a favorable reception",page x and led to a book, Why We Get