Intellectual Disability (ID): An Overview from History, Terminology, and Classification to Recent Trends

History Of Intellectual Disability

Intellectual Disability (ID, also known as mental retardation) is a condition of arrested or incomplete development of the mind. ID is especially characterized by impairment of skills manifested during the developmental period, which contribute to the overall level of intelligence, i.e. cognitive, language, motor, and social abilities (WHO, 1992). It occurs in 2-3% of the general population. Prevalence of mild level of intellectual disability is seven to ten times more than severe level of intellectual disability.

The understanding about intellectual disability, mainly its features, causes and intervention has a long history. Both modern and ancient cultures presumed that demon possession caused ID. Similarly, some cultures thought ID was a punishment by God. There were some exceptions. As early as 1500 B.C. some physicians understood IDs as a medical problem. Although translation is imprecise, the therapeutic papyri of Thebes (Luxor), Egypt, 1500 B.C. reference disabilities of the mind due to brain damage. Ancient Greeks and Romans looked upon the condition as a burden on society. Accordingly, persons with ID were treated atrociously. The ancient Greeks and Romans commonly killed infants believed to be defective. Others were sold for entertainment. Since demonic possession or God's wrath was believed the cause, they were treated as less than human. (Reynolds, Zupanick, &Dombeck,2013).

Not much literature is available on mentioning intellectual disability in the past, especially prior to 1700. Jean-Marc Itard (1774-1838) is considered as the pioneer of systematic instruction for intellectually disabled as he tried to educate the boy named Victor with cognitive impairment. The special education for less abled children slowly gained popularity and Edouard Seguin (1812-1880) established an educational program in Paris which emphasized physiological and moral education.One of the major changes occurred in the history of Intellectual disability is the Eugenics movement in the late 19^th century. “Eugenics” comes from the Greek words for “good” and “origin,” or “good birth” and it is a social philosophy advocating the improvement of human genetic traits through the promotion of higher rates of sexual reproduction for people with desired traits (positive eugenics), or reduced rates of sexual reproduction and sterilization of people with less-desired or undesired traits (negative eugenics), or both ( Osborn &Frederick,1937).The term eugenics was first coined by Francis Galton in the late 1800’s and he believed that desirable traits could pass through generations based on his studies on intelligence among upper class of Britain. He found that their desired traits such as superior intelligence are hereditary and passes through generations and favored the idea of selective breeding or humanity could be improved by encouraging the fittest members of society to have more children (Norrgard, 2008).The movement became popular in America in the early part of 20^th century and it resulted in a negative attitude towards disabled people including mentally ill and intellectually disabled or feeble-minded individuals as they were considered to polluting the gene pool of the country.Such individuals were seen as a threat to society and the probable cause of most of the criminal activity and social problems of the country. In many states, support for the Eugenics movement resulted in legislation requiring mandatory sterilization, incarceration, and in many cases, the castration of persons with disabilities. In each state, hundreds of thousands of people with mental illness or intellectual disabilities were placed in institutions, the largest of which housed as many as 20,000 people(Felty, 2007).

In addition to this, the development of intelligence tests also made remarkable contribution in the history of Intellectual disability. During the early 1900s, Alfred Binet and Theodore Simon developed the first intelligence test as result of the request by the French government to find students with academic difficulties in the school. Terman standardized this test with sample from America and published in 1916, was called the Stanford-Binet Intelligence Scale. Psychological testing, especially intelligence tests used to identify intellectual deficiency and institutionalization was considered as the major remedy for the problem of intellectual disability.On his study on Kallikak family, Goddard (1912) found that feeblemindedness” was inherited which also encouraged institutionalization and sterilization of intellectually disabled people.