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to be divine punishment of the parents； or possessed by Satan。
As society became somewhat more humane； institutions for the “feeble…minded” were established；
though the lifestyle of these individuals did not necessarily improve as a result of such institutions。
These individuals lived out their short lives in drab and often punitive surroundings。 Many were
victims of genocide。 Hitler’s goal to purify the Aryan race serves as a chilling exemplar of this issue。
It is estimated that 300；000 developmentally delayed or disabled individuals were killed under
Hitler’s leadership。
Until recent years； developmentally delayed or disabled individuals were classified as morons；
imbeciles； or idiots； depending on the extent of disability。 The genetic disorder we now call Down
syndrome was called Mongolian idiocy。 The genetic disorder known currently as Tay…Sachs
disease was called amaurotic family idiocy。
The situation for the developmentally delayed/disabled individual began improving in the 1960s。
President Kennedy spoke out for these individuals； and was instrumental in making funds
available for research in this area and education for the developmentally delayed or disabled。 The
zeitgeist of the 60s emphasized environmental factors in intelligence and challenged the view that
low intelligence is genetically programmed。
Developmental delay or disability is difficult to define and； at one point in time； the diagnosis was
made entirely based on IQ scores。 Today； the child’s adaptive capacities are also considered in
assessing the intellectual capabilities of the child。 Consideration is given to the fact that the
individual’s self…help skills； socialization； language； and motor skills are significantly less well…
developed than those of normal children of the same age。 There remains a fuzzy boundary； between
the “almost developmentally delayed or disabled” and the “just barely delayed or disabled。” It is
estimated that about 3 percent of children are diagnosed as being developmentally delayed or
disabled。 A diagnosis of developmental delay or disability is not made after age 18。
Mild Mental Retardation。 Mildly developmentally delayed or disabled children have an IQ of
between approximately 50 and 75； and these account for approximately 80 percent of all the
developmentally delayed individuals。 Mildly delayed/disabled children can learn to read and
write and to do simple arithmetic。 They learn slowly and have great difficulty with abstract
concepts。 Their disability is most noticeable in school。 As adults； they hold jobs and live
independently； often overing the stigma of retardation。
Moderate Mental Retardation。 Moderately delayed/disabled children have an IQ between 35 and
55。 About 12 percent of developmentally delayed/disabled children fall into this category； many of
them are Down syndrome children。 Whereas the mildly the delayed/disabled individual is
described； as “educable；” the moderately delayed/disabled child is described as “trainable。” These
children use language and can learn self…help skills； and their training involves teaching of skills
that will enable them to have a degree of independence in the munity。 Many of them learn to tell
time； to count money； and to find their way around in the environment。
Severe Mental Retardation。 Severely delayed/disabled children have an IQ of 20 to 35。 They can
learn some language and self…help skills。 Most of these children are institutionalized。 About 8
percent of people with an IQ below 70 are severely delayed/disabled。
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CHAPTER 10： INTELLIGENCE AND INTELLIGENCE ASSESSMENT
Profound Mental Retardation。 These children have an IQ of less than 20； and require supervision
and nursing care all their lives。 About 1 percent of delayed/disabled children are profoundly
retarded。
It is probably more meaningful to classify the developmentally delayed or disabled individual
according to the cause of their retardation。
Genetic causes。 Down syndrome is the result of a genetic aberration （it is not a hereditary problem）
that results in three chromosomes at the 21st position rather than two。 It is the most mon
genetic cause of retardation； and occurs in approximately one of every 1；000 live births。 The
incidence of this disorder has decreased as a function of the ability to detect it through
amniocentesis and chorionic villi sampling。 The next most mon genetic cause of retardation is
phenylketonuria （PKU）； a metabolic disease carried by a recessive gene。 It can be detected shortly
after birth and controlled。 There are a number of other relatively rare genetic causes of mental
retardation； including Tay…Sachs disease； Klinefelter’s syndrome； and Niemann…Pick disease。
Intrauterine infection or trauma。 Infections contracted by the mother can cause mental retardation。
These causes include encephalitis； rubella； and syphilis。 Brain damage to the fetus can also result
from malnutrition and dietary deficiencies； poisoning by lead or carbon monoxide； or drug use by
the mother； especially alcohol； during the mother’s pregnancy。 Recent evidence supports a
correlation between use of crack cocaine and fetal injury。
The birth process。 Premature children sometimes have an immature nervous system； and anoxia
（oxygen deprivation） or head injury during birth can damage the brain and cause mental
retardation。 All of these causes together probably account for no more than 30 percent of all cases of
developmental delay/disability； and all have identifiable physical causes。 In many cases； these
children have physical deficiencies and deformities in addition to their retardation。 It is striking to
note how many of such cases could be prevented or avoided； given appropriate prenatal care of the
mother； and the mother’s knowledge and acceptance of her responsibility to protect her unborn
child。
Cultural—familial causes。 The majority of cases of retardation fall into this category。 Children in
this category are usually mildly delayed or disabled。 Usually； they do not have other physical
handicaps and generally do not look any different from normal children。
Cultural—familial retardation is most likely to occur among the children of the poor； often in
families that have struggled against poverty for several generations。 There are often several
developmentally delayed or disabled individuals among the relatives； and sometimes one or both of
the parents is or are delayed or disabled。 In cultural—familial retardation； it is difficult to separate
the effects of heredity and environment； because neither is favorable。 Many psychologists currently
think that heredity sets an upper limit； and that environment determines how closely an individual
will approach his or her maximum intellectual capacity。 For example； in the case of a child with
cultural…familial retardation； the genes may set a limit of 80 or 90； or higher； but because of lack of
language and cognitive stimulation； his or her test score could be 60 or 65。
The study of the Hollow Children is highly instructive。 There was a group of people of English and
Scots…Irish descent who settled and lived as a little subculture near the Atlantic coast in Virginia for
many years。 The land they lived on was subsequently granted to German immigrants and the Scots…
Irish were forced to move into hollows in the Blue Ridge Mountains。 They formed a number of small
munities that varied in degree of isolation from civilization。 In 1932； an investigator named
Sherman studied these people； reasoning that the citizens of the various Hollows munities had
a mon gene pool； and he was interested in whether isolation from civilization had affected the
intellectual ability of the children。 Isolation meant things like no road in and out； no post office； no
newspapers or magazines； and； of course； since the study was done in the early 1930s； there was no
radio or TV。 In Colvin Hollow； the most isolated of the munities； school had been in session for
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PSYCHOLOGY AND LIFE
a total of 16 months during the years between 1918 and 1930； and there were only three literate