Intelligence – Extremes and
Influence
RG 11c
Extremes of Intelligence
A valid intelligence test divides two groups of
people into two extremes. The mentally retarded (IQ
70) and individuals with high intelligence (IQ 135)
are significantly different.
Intellectual Disability
(formerly Mental Retardation)
Mental retardation – having significantly belowaverage intellectual functioning and limitations in at
least two areas of adaptive functioning
Adaptive functioning includes…
● communication skills
● self direction
● self-care
● health and safety
● ability to live independently
● academics
● social skills
● leisure and work
● community involvement
Intellectual Disability
Causes – various factors…
● genetics (down syndrome)
● environmental (fas, sbs)
● deprivation or neglect
● no apparent/known cause
Cure – none, yet some preventative measures for
certain types of MR…
● test performed on newborns tests for hidden genetic
disorder called PKU…if detected early, the MR
associated with PKU can be prevented by a special diet
● more generally…genetic counseling, pregnancy care
services and education of new parents are other
Intellectual Disability
Levels of ID/MR…
Mild (50-70) – 85% of all MR – academic abilities at approx. 6th
grade level…can learn to live on own and hold a job
Moderate (35-49) – academic abilities approx. 2nd grade level –
can be trained in self-care and acquire some reading/writing
skills, yet need some supervision
Severe (20-34) – mental capacity of approximately a 5-year-old –
learn to talk in most cases and perform simple tasks, yet need
close supervision
Profound (below 20) – mental age less than 3 – very limited
communication and require constant supervision…usually have
Intellectually Gifted
Intellectually gifted – have IQ scores above 130-135
Most extensive research on “giftedness” was done by
Terman...resulting data much of what we know about
subject
●studied 1528 students near top of IQ
range into adulthood
●found that gifted children excelled in
school, had overall good health, were
generally happy (newer research
suggests that highly gifted children may
be susceptible to certain physical or
psychological disorders)
Genetic and Environmental
Influences on Intelligence
No other topic in psychology is so passionately
followed as the one that asks the question, “Is
intelligence due to genetics or the environment?”
Genetic Influences
Studies of twins, family members and adopted
children together support the idea that there is a
significant genetic contribution to intelligence.
Genetic Influences
Studies of twins have pointed toward genetic influences…
● Minnesota Twins Project – U of Minn – James Bouchard
o Focused on identical twins reared-apart
o In 1979, Bouchard came across an account of a pair of twins (Jim
Springer and Jim Lewis) who had been separated from birth and were
reunited at age 39. "The twins," Bouchard later wrote, "were found to
have married women named Linda, divorced, and married the second
time to women named Betty. One named his son James Allan, the other
named his son James Alan, and both named their pet dogs Toy."
o Research still ongoing…studied over 100 pairs of identicals
separated at birth…all with similar results, much of
personality, temperament, intelligence, etc. the same or very
Genetic Influences
Other research supporting genetic influences…
● Studies of identical twins have shown a stronger
correlation in IQ scores when compared with fraternal
twins
● adopted children tend to have a more similar IQ to their
biological parents, rather than adoptive parents
● research coming out of Human Genome Project has also
suggested that intelligence has a genetic component
scientists point out that a genetic basis of intelligence is
complex however because it involves the interaction of
many genes
Environmental Influences
Studies of twins and adopted children also show:
●Greater similarity in IQ scores of those individuals
reared together than those reared apart…
Questions on twin studies and
intelligence
If genetic factors play an important role in development of intelligence
as measured by an IQ test, then which of the following statements is
most likely to be true?
A. The IQ scores of parents and their offspring will be more nearly
alike than IQ scores of identical twins.
B. The IQ scores of siblings reared together will be more nearly
alike
than IQ scores of identical twins.
C. The IQ scores of fraternal twins reared together will be more nearly
alike
than the IQ scores of identical twins reared apart.
D. The IQ scores of fraternal twins will be equivalent in similarity to
the IQ scores of identical twins.
E. The IQ scores of identical twins reared apart will be more nearly
alike than the IQ scores of fraternal twins reared together.
Cont'd...
Jim and Tim are identical (monozygotic) twins that were reared
together. Scott and Michael are fraternal (dizygotic) twins that were
reared together. Given the results of heritability studies of intelligence,
which of the following outcomes are most likely to emerge?
A. Jim and Tim will have very similar IQ's.
B. Scott and Michael will have very similar IQ's.
C. Both pairs will have very similar IQ's.
D. Neither pair will have similar IQ's.
E. Jim and Michael will have similar IQ's.
Schooling Effects
Schooling is an intervention that pays dividends,
reflected in intelligence scores. Increased schooling
is related to higher intelligence scores.
To increase readiness for schoolwork
Projects like Head Start facilitate leaning.
Reasons for Why Environment
Affects Intelligence
1.The races are remarkably alike genetically.
2.Race is a social category.
3.Asian students outperform North American students
on math achievement and aptitude tests.
4.Today’s better prepared populations would
outperform populations of the 1930s on intelligence
tests.
5.White and black infants tend to score equally well on
tests predicting future intelligence.
6.In different eras, different ethnic groups have
experienced periods of remarkable achievement.
Controversy…
Studies have been done comparing different
ethnicities, social classes and adopted children,
trying to prove impact of genetics or environment on
the scores of these different groups
● No solid evidence has come about either way…some
evidence suggests that environmental changes can
influence IQ scores of children in “deprived situations”
● Studies also show that there are
probably test biases for children
of lower socioeconomic and
minority groups due to the norms
of most IQ tests being based on scores
Genie Wiley
Heritability
Heritability – the amount of trait variation within a
group that can be attributed to genetic differences
●HERITABILITY AND HEREDITY ARE NOT THE
SAME…heritability is looking at differences in
groups where heredity is looking at an individual’s
traits
●You can only speak of heritable differences within
a group of individuals who have shared the same