Research is being conducted to determine the genetic origins or biological factors of various disorders. Genes have been shown to be associated with the origin of schizophrenia and Alzheimer's Disease. Depression is known to be associated with changes in brain chemicals. Alcohol dependence, often branded as a vice resulting from poor moral character, is now linked to both the social environment and to genes. One biological cause of mental retardation is the lack of iodine, vital for brain development, in the diet of a growing child.
Social influences can significantly contribute to the development of various disorders.
For example, individuals react differently to stressful situations. Loss of a loved one can potentially lead to depression. Loss of work is associated with heavy alcohol use, suicide and depression. Poor nurturing environments, whether the result of broken families or violence in the home or community, can result in an increased risk of mental illness. In some societies, mental illnesses are thought to be caused by evil spirits.