2.2 Genetics and behaviour
What is intelligence quotient (IQ)?
Should indicate one’s genetically endowed
intellectual potential
Answer questions in groups of 4:
Do you think that these tests appropriately
evaluate your intelligence?
Do you feel that the tests were adequate? Why
or why not?
How would you change the tests to make them
reflect more accurately what you consider to be
your “intelligence”?
Alfred Binet a pioneer in intelligence research,
beginning of the 20th century
 Pr. Richard J. Herrnstein
& Charles Murray 1994,
Harvard: The Bell Curve
- The Bell Curve is a best-selling but
controversial 1994 book. Its central argument is
that intelligence is a better predictor of many
personal dynamics, including financial
income, job performance, chance of unwanted
pregnancy, and involvement in crime than are
an individual's parental socioeconomic status,
or education level. The book also argues that
those with high intelligence, the "cognitive
elite", are becoming separated from those of
average and below-average intelligence, and
that this is a dangerous social trend.
What is it?
How can it be measured?
Charles Spearman – theorized that there is a
general intelligence factor, which he called the
“g” factor.
Modern intelligence testing attempts to assess
this “g”
But the question is: where does “g” come from?
Bouchard and McGue (1981) reviewed 111
studies of IQ correlations between siblings
A meta-analysis
Results: the closer the kinship, the higher the
correlation for IQ
The Minnesota Twin Study by Bouchard et al
Longitudinal study since 1979 & cross-cultural
MZA (identical twins raised apart) compared
to MZT (identical twins raised together)
The mean age was 41 years (start of the study),
differ from most other research which is
carried out on adolescents
Each twin completed 50 hours of testing and
The concordance rates of intelligence can be
found in a table on p. 55
The study concluded that 70% of intelligence
can be attributed to genetic inheritance – leaves
30% to other factors
Media coverage to recruit participants
Ethical concerns – reunited the twins
No adequate control to establish the frequency
of contacts between the twins prior to the study
“equal environment assumption”
Scarr and Weinberg (1977) and Horn et al
(1979) studied parents who raised both
adopted and natural children
So same environment – any differences should
be due to… what?
Found no significant difference in IQ correlations!
Very interesting findings
Another study by Wahlstein (1997) found that
transferring children from low socio-economic
status family to one where they are high socioeconomic status improved childhood IQ scored by
12-16 points (about one SD)
Shows that an enriched environment may raise IQ
in children.
Does this resemble to something else we studied?
Women and Math stereotype threat:
Stereotype threat:
Found out (p.56) and answer in writing:
What is eugenics?
What is the Less effort hypothesis?
Does IQ change over time?
Which factor is the most important
environmental factor in development of IQ?
Why has the average mean on IQ tests been
going up over the years?

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