There are multiple variations on disengagement theory, such as moral-disengagement theory. The disengagement theory of aging states that "aging is an inevitable, mutual withdrawal or disengagement, resulting in decreased interaction between the aging person and others in the social system he belongs to". The theory claims that it is natural and acceptable for older adults to withdraw from society. The theory was formulated by Cumming and Henry in 1961 in the book Growing Old, and it was the first theory of aging that social scientists developed. Thus, this theory has historical significance in gerontology. Since then, it has faced strong criticism since the theory was proposed as innate, universal, and unidirectional.