Individual
Differences
Intelligence
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Nature vs Nurture
in Intelligence
Last updated:
10 Apr 2005
Overview
Nature vs. Nurture - What do you think?
Pendulum of opinion on Nature vs. Nurture through history
Historical trends in the nature-nurture debate
Evidence in favour of nature
Evidence in favour of nurture
The role of interaction
What have we learnt about intelligence?
Final quotes
References
Overview
The issue of what causes individual differences in intelligence goes beyond psychology,
and involves moral, political, ethical, educational, social, physiological and statistical
issues to name just a few. The issue of how differences in intelligence come about
between individuals and groups is a topic of much fascination and controversy - it can
arouse strong reactions and elicit personal beliefs and biases.
This page outlines some of the main psychological concepts and evidence that relates to
explaining individual differences in intelligence.
As a student, it is your responsibility to develop a familiarity with the basic arguments,
strengths, and weaknesses for and against the causal influences and correlates of
intelligence.
Nature vs Nurture - What do you think?
In looking for the causes of individual differences in intelligence, a major issue is the
relative contribution of genetics and environment.
100 90% 80% 70% 60% 50- 60% 70% 80% 90% 100
% Gen Gen Gen Gen 50 Env. Env. Env. Env. %
Gen .
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.
Envi
etics
ron.
(Nat
(Nur
ure)
ture
)
Rate the extent to which you believe nature and nature influence (cause) human
intelligence.
Warning!
As you learn more about the theory and research on genetic and environmental influences on human intelligence, you may find that
you change some of your beliefs and assumptions.
Pendulum of opinion on Nature vs. Nurture through
history
The zeitgeist (the intellectual and culture "flavor" of a time and place) has swung back
and forth over time with regard to the amount of influence that nature vs. nature has on
human intelligence.
 For example, in the late 1800's in the UK, as Darwinism took off, the role of
genetically determined capability was considered very important.
 This was in constrast, for example, to the 1960's in the USA, when views were
more in favor a "tabula rasa" (blank state) view of human intelligence - in other
words, all people are capable of much more, if given conducive environmental
conditions in which to reach their potential
 Currently the Zeitgeist is the Western psychological world is somewhere
inbetween - both genetics and environment are seen as playing important roles. To
be more precise, the modern view about nature vs nurture in intelligence is
"interactionist". This view is well expressed by Ridley (1999, p.77):
"Mother Nature has plainly not entrusted the determination of our
intellectual capacities to the blind fate of a gene or genes; she gave us
parents, learning, language, culture and education to program ourselves
with."
Historical trends in the nature-nurture debate
Late 19th century - early 20th century (Nature)
From the mid to late 1800's through to the early 1900's opinions rested in the nature
camp. This was consistent with the scientific discoveries of the role of inheritance and
natural selection by Mendel and Darwin.
The major contributor to the psychological argument was Francis Galton in his book
"Hereditary Genius: Its Laws and Consequences” (1869).
Galton had observed that the gifted individuals tended to come from families which had
other gifted individuals. He went on to analyze biographical dictionaries and
encyclopedias, and became convinced that talent in science, the professions, and the arts,
ran in families.
Galton took this observation one step further, to argue that it would be "quite practicable
to produce a high gifted race of men by judicious marriages during several consecutive
generations".
This suggestion became know as eugenics, "the study of the agencies under social control
that may improve or repair the racial qualities of future generations, either physically or
mentally." Galton wanted to speed up the process of natural selection, stating that: "What
Nature does blindly, slowly, and ruthlessly, man may do providently, quickly, and
kindly”.
Galton was convinced that "intelligence must be bred, not trained". Such arguments have
had massive social consequences and have been used to support apartheid policies,
sterilization programs, and other acts of withholding basic human rights from minority
groups.
Post WWI: 1920s-1930s
After World War I, careful reanalysis of the mass of intelligence test data took place. This
began to challenge the commonly held view that intelligence was directly, genetically
linked to racial differences:
 e.g. blacks from Illinois had higher IQ scores than whites from 9 southern states a finding difficult to reconcile with the simple idea that whites are intellectually
superior to blacks.
Evidence now seemed to support a closer link between social class and intelligence,
rather than race and intelligence. As a result, a number of psychologists in the 1920s and
1930s shifted their position towards the environmental camp.
The shift against 'nature' views was given momentum by the backlash against the social
consequences of government policies:
 e.g. sterilization laws had been passed in 24 US States, resulting in 20, 000 people
being sterilized against their will. 320, 000 people suffered the same fate in
Germany.
1940s-1990s
The backlash faded, and the pendulum swung back towards the middle. From the early
1940's, it seemed there was a rejection of simplistic nature or nurture views, with more
common recognition of their complex interplay. Nevertheless, social prejudices and
inequalities were still evident and growing.
Thus, in the 1960's, the focus of the problem was shifted away from the individual as the
cause of the problem, and centered on social determinants. Thhe pendulum swung
towards the nurture/environmental end and away from the nature/genetic end. Efforts
were made to arrest poor educational achievement through special schooling, and to
alleviate poor living conditions through welfare.
It became politically correct to minimize talk and discussion of the role of 'nature' in
contributing to any individual differences, let alone intelligence. The evidence of
differences in intelligence between socioeconomic groups and racial groups, however,
did not go away.
Recent trends - "The Bell Curve" controversy
From time to time, there have been inflammatory articles which present and interpret
evidence of IQ differences between groups (in particular Jensen, 1969). The most recent,
and most major of these publications was Herrnstein and Murray's (1994) "The Bell
Curve". This book provided momentum to swing the pendulum in the direction of
'nature', at least in the public's eye, but even more so, it generated massive debate and
controversy in psychology, sociology, education, and politics, not to mention the media
and household. The 800+ page book, written for laypersons, hit the best-seller lists in the
U.S.
"The work's main thesis is that an individual's intelligence - no less than 40%
and no more than 80% of which is inherited genetically from his or her
parents - has more effect than socioeconomic background on future life
experiences."
Manolakes (1997), p.235
In addition to the premise that measured intelligence (IQ) is largely genetically inherited,
a second important premise was that IQ is correlated positively with a variety of
measures of socioeconomic success in society, such as a prestigious job, high annual
income, and high educational attainment; and is inversely correlated with criminality and
other measures of social failure. It was suggested that SES successes (and failures) are
largely genetically caused.
Some sample controversial quotes from "The Bell Curve"
 “IQ has more effect on future life experiences than SES”
 “intervention efforts are largely a waste of time and money”
 “increasing population of 'lower caste' intelligences, lessening the
nation's 'genetic capital”
Reactions to The Bell Curve:
 The Bell Curve" re-ignited the nature-nurture debate.
 The public debate was (and is) divided.
 The politically left saw the authors as "un-American”;- "pseudo-scientific
racists”;- and the book as "alien and repellent"
 The politically right saw the authors as:
- "brave and respectable scholars,”;- whose book was "lucid" and
"powerfully written"
 The part of The Bell Curve that captured public attention was on the differences
in IQ between African and Caucasian Americans. Further to this were the
suggestions made by Herrnstein and Murray about the implications of a
predominantly genetically-inherited intelligence for public and social policy.
Since IQ was largely seen as genetically determined, the authors expressed
resistance to educational and environmental interventions. They argued that
money spent in this way is wasted. The authors also argued that America is
becoming a society of 'cognitive castes', with the lower caste including a large
proportion of African-Americans. Hence their statement that the 'genetic capital'
of society is being eroded because the less intelligence, lower class is reproducing
at a greater rate than high IQ classes.
Evidence in favour of nature
In the heyday of eugenic IQ testing in the 1920s there was no evidence for the heritability
of IQ. It was just an assumption of the practitioners. Today that is no longer the case. The
heritability of IQ (whatever IQ is!) is now an hypothesis that has been tested - on twins
and adoptees. The results really are quite startling. No study of the causes of intelligence
has failed to find a certain and often substantial heritability. What varies from study to
study is the amount that can be attributed to heritability.
Concordance rates of IQ scores
 Evidence from family studies provides the main supporting evidence from which
arguments about the relative roles of genetics and environment are constructed.
A large number of the study of twins reared apart was undertaken by Thomas
Bouchard of the University of Minnesota starting in 1979. He “collected” pairs of
separated twins from all over the world and reunited them while testing their
personalities and IQs. Other studies at the same time concentrated on comparing
the IQs of adopted people with those of their adopted parents and their biological
parents or their siblings. Put all these studies together, which include the IQ tests
of tens of thousands of individuals, and the table looks like this:
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Same person tested twice 87%
Identical twins reared together 86%
Identical twins reared apart 76%
Fraternal twins reared together 55%
Biological siblings reared together 47% (studies show that reared apart about
24%)
Parents and children living together 40%
Parents and children living apart 31%
Adopted children living together 0%
Unrelated people living apart 0%
Ridley, 1999, p.83 [The number is a percentage correlation . Attach section from
Ridley's book.]
Meta-analytic estimates of the heritability of intelligence
A meta-analysis of 9 family studies was conducted by Daniels, Devlin and Roeder
(1997): it included 212 correlations and produced very similar results to those quoted by
Matt Ridley. These authors conclude that heritability can account for 48% of the
variation in IQ. The highest estimates have come from reviews of research by Herrnstein
& Murray, 1994 (74%) and Eysenck (80%). A safer bet is probably to sit on the fence 50:50!
Heritability indices, however, are not pure measures of genetic inheritance - they
included prenatal environmental influences, (e.g. whether the mother smokes, what she
eats, etc.) and the postnatal material environment. Thus these heritability indices are
likely to overestimate the role of genetics.
Correlation of child-parent verbal ability scores
This graph shows correlations between children and their parents and adopted children
and their biological and adoptive parents on verbal ability scores.
Heritability & intelligence
It must be noted, however, that heritabilty is not pure genetic influence as the pre and
postnatal environments must be taken into account. Heritability estimates based on
comparing correlations between IQs of monozygotic (identical) twins reared together
with IQs of dizygotic (fraternal) twins and siblings are likely to overestimate the genetic
component because monozygotic twins share more similar environments - both in the
womb and out
 twins reared apart are not assigned at random to foster or adoptive parents - since
homes are selected purposely to with regard to characteristics of the child and
characteristics of the family. This would partially account for the IQ correlations
attributed to inheritance
 twin studies may not be generalizable to the population at large as twins are more
susceptible to prenatal trauma leading to retardation. The inclusion of retarded
cases may increase the twin correlation in intellligence test scores.
heritability indexes refer to the population on which they were found at the time
and is not applicable to an analysis of test performance between two population
groups e.g. ethnic groups.
 heritability does not indicate the degree to which a trait can be modified e.g. even
if the heritabilty of a trait, like intelligence were found to be 100% it wouldn't
mean it couldn't be modified. (Anastasi & Urbina, 1997).
In the discussion to date, we have focused on the heritability (or otherwise) of general
intelligence. What about the subcomponents of intelligence? There is, indeed, evidence
of a greater genetic link for:
1. Spatial ability
2. Reasoning
And less evidence for genetic influence on:
1. Divergent thinking
2. Verbal fluency
There is, however, relatively little research along these lines.
Evidence in favour of “nurture”
"Give me a dozen healthy infants & my own specific world to bring
them up in, & I'll guarantee to take any one at random & train him to
become any type of specialist I might select - doctor, lawyer, artist,
merchant, chef & yes, even beggar & thief, regardless of his talents,
penchants, tendencies, abilities, vocations, and race of his ancestors."
- John B. Watson, 1924
This was a famous quote in the heyday of behaviorism, when the child was considered to
be a 'tabula rasa' (blank slate) onto which anything could be sculpted through
environmental experience. This would be a 100% environmental view, but virtually no
psychologists would accept such an extreme position today.
The Flynn effect: Are we getting smarter?
In the 1980s, a NZ-based political scientist, James Flynn, noticed that IQ was increasing
in all countries all the time, at an average rate of about 3 IQ points per decade i.e. the
average IQ across the world has risen over 1 standard deviation (i.e. 15 points) since
WWII - predominantly due to environmental effects. As a result, new norms continue to
be used to rescale IQ tests to '100'.
Could this be due to diet? Possibly but IQ scores are still rising just as rapidly in wellnourished western countries. Could it be schooling? Interruptions to schooling only have
temporary effects on IQ. Importantly, it is those tests that test abstract reasoning ability
that show the steepest improvements. One researcher, Ulric Neisser suggests that the
Flynn effect is due to the way we are being saturated with sophisticated visual images:
ads, posters, videogame and TV graphics etc - rather than written messages. He suggests
that children experience a much richer visual environment than in the past and that this
assists them with visual puzzles of the kind that dominate IQ tests.
The evidence for the rise in IQ comes from:
- Adoption studies
- Nutrition studies
- Educational intervention studies
Intelligence varies with at least 21 factors
Some of the other circumstances and attributes that have been found to vary to a greater
or lesser (but always significant) extent in relation with IQ (Bouchard & Segal, 1985;
Liungman, 1975) - note that not all of these relationships support an environmental view.
Intelligence varies with:
 Infant malnutrition (-ve)
 Birth weight
 Birth order
 Height
 Number of siblings (-ve)
 Number of years in school
 Social group of parental home
 Father's profession
 Father's economic status
 Degree of parental rigidity (-ve)
 Parental ambition
 Mother's education
 Average TV viewing (-ve)
 Average book-reading
 Self-confidence according to attitude scale measurement
 Age (negative relationship, applies only in adulthood)
 Degree of authority in parental home (-ve)
 Criminality (-ve)
 Alcoholism (-ve)
 Mental disease (-ve)
 Emotional adaptation
"No single environmental factor seems to have a large influence on IQ. Variables widely
believed to be important are usually weak....Even though many studies fail to find strong
environmental effects....most of the factors studied do influence IQ in the direction
predicted by the investigator....environmental effects are multifactorial and largely
unrelated to each other."
- Bouchard & Segal (1985), p.452
So, it would appear that there are many psychological and biological factors each
contributing a small a small fraction to the variance in IQ scores.
Intelligence & race
Let's focus on some of the correlates of intelligence examining in particular the interplay
between race, environment and intelligence; between SES, environment and intelligence;
between education, environment and intelligence; and between occupation, environment
and intelligence.
Herrnstein and Murray (1994) in The Bell Curve state that :
- Asians and Asian-Americans have a (.32 standard deviation) higher average IQ than
white Americans, and that
- white Americans have a (1.58 standard deviation) higher mean IQ than black
Americans.
Further, they claim that this difference is not a function of cultural testing bias.
Herrnstein and Murray (1994) acknowledge that the causes of these differences could be
environmental, however the differences in IQ appear to be too large to be accounted for
by environmental influences alone. They provide much qualification, cautioning, and
warnings about how their evidence should be interpreted and used. In particular, they
remind the reader that
- IQ is not strongly linked to many so-called 'desirable' human qualities; and
- The fallacy of drawing conclusions about individual on the basis of group findings.
It would be incorrect to characterize "The Bell Curve" as out-and-out a racist, eugenicist,
etc. book. Even detractors acknowledge the importance of its contribution to
psychological and social debate. But the book does, in general, support a view that
intelligence is largely heritable.
Note that there have also been investigations into racial differences on subcomponents of
intelligence. Herrstein and Murray (1994) report that:
- East Asian scores are typically the same or slightly lower than White American scores
on verbal IQ, but much higher on visuo-spatial IQ
- Black Americans tend to score higher than whites on subtests involving arithmetic and
immediate memory, whereas whites typically score high than blacks on subtests of
spatial-perceptual ability
Differences in IQ scores between races does not necessarily imply genetic causes. Most
psychologists accept that there are group mean differences in IQ scores for nonculturally-loaded tests. However, these differences are confounded with the effects of
SES, e.g.
1. Children with black fathers, brought up in white family - no evidence of lower IQs
2. Adoption studies - e.g. black children brought up by white families only slightly lower
IQs than white adopted children (Howe, 1997)
Some theorists suggest that socioeconomic disadvantages are the main causes of ethnic
differences in IQ.
Even if the variation within a group reflects genetic differences, the average differences
between the groups could be wholly due to environmental factors. Imagine, two pots,
with randomly allocated seeds from the same batch. The two pots have equivalent
genetic potential. One pot received fertilizer (an environmental condition), the other pot
receives no fertilizer. The average height (i.e. intelligence) differences between each pot
will be due to environmental differences (fertilizer), however the height differences
amongst individual plants within a pot are due to genetic differences (assuming similar
conditions throughout the pot).
There is debate about whether heritability estimates even matter, since they can't be
applied to an individual or be used to help people:
Wahlsten (1997, p. 84) states that:
"It does not matter whether the field of human behavior genetics finally
decides that the heritability of IQ in the United States is 25%, 40%, 50%, or
70%. Any such estimate will be utterly useless to anyone seeking better ways
to improve the intelligence of the nation through health care and education."
Intelligence & socioeconomic status
Herrstein and Murray (1994) argue that low intelligence causes low SES, rather than the
other way around. So, according to these authors, while SES is correlated with IQ, it
should be considered a consequence rather than a cause.
However, adoption studies seem to indicate that SES has a strong, causal effect on
intelligence, e.g.:
"Well-controlled adoption studies done in France have found that transferring
an infant from a family having low socioeconomic status (SES) to a home
where parents have high SES improves childhood IQ scores by 12 to 16
points or about one standard deviation, which is considered a large effect size
in psychological research." Wahlsten (1997, p. 76).
Several recent US studies have demonstrated improvements in children's IQ's by
improving the lives of infants in disadvantaged circumstances.
These studies employed random assignment of children and families to treatment and
control conditions.
These studies selected families with:
� low parental IQ
� low parental education
� minimal financial resources
Experimental group received:
� enriched, educational day care outside the home every weekday from 3 months to start
of schooling
Control group received:
� nutritional supplements and pediatric medical care or crisis intervention but no
educational day care
Even though the children returned to their home environment every day and spent
holidays and weekends with their families (mostly unemployed, single mothers) in
poverty-stricken neighbourhoods, there were large gains in IQ; almost as much as in the
French studies previously mentioned.
Furthermore, the mean IQ of the enriched groups appeared to be quite typical of healthy
American children. These children continued to show higher IQ scores than controls at
age 12 (Wahlsten, 1997). Of course, in these American studies, SES and education were
being manipulated. There is of course a strong correlation between SES and education in
both directions.
Intelligence & education
A number of studies have shown that schooling and intelligence influence each other.
Higher intelligence tends to lead to prolonged schooling and longer schooling leads to
higher IQ.
Intelligence at age 5 predicts better than any other variable a child's future educational
progress and attainment (Kline, 1991).
Wahlsten (1997):
� delays in schooling cause IQ to 'drop' 5 points per year
� temporary drop in IQ during school vacations
Winship & Korenman (1997):
� 2.7 IQ point advantage for each year of schooling
� thus to predict later IQ, two estimates are useful: early IQ estimates and number of
years of schooling
A study by Cahan and Cohen, found that older children in a grade tended to score slightly
higher than their younger classmates but importantly they found that children who are in
a higher grade but are virtually the same age as children in the grade lower have higher
IQ scores. It is postulated this is due to the extra year of schooling.
However a number of authorities believe that enriched or increased schooling has little
effect on intelligence and have refute the suggestion that intelligence can be modified.
"Compensatory education has been tried and it apparently has failed."
- Jensen, 1969
"the story of attempts to raise intelligence is one of high hopes, flamboyant claims, and
disappointing results."
- Herrstein & Murray (1994), p.389
One justifiable criticism levelled at educational enrichment studies conclusions about
increased IQ is that what is being modified is performance on a test rather than an actual
modification in intelligence. Children in enrichment programmes often receive extensive
instruction and practice in test-taking. “What has been temporarily modified in the early
stages of early intervention programmes is performance on a test, not the child's general
intelligence” (Herman Spitz, 1999, p. 289).
This would account for the well-known fade-out effect, whereby initial, often very high
gains in IQ scores, in experimental “enriched schooling” groups, return to the level of the
control group a few years after the “experiment”.
In the US a large nationwide programme, the Head Start programme, aims to enrich the
schooling of disadvantaged children. On the whole, the results have been mixed. Head
Start and programmes like it have been criticized for not living up to expectations in
changing IQ. The main defense is that the primary aim is not to improve IQ, but to
accelerate academic development - IQ change is a bonus, academic development is more
important.
Head Start type programmes have also been criticized for not effecting last changes. This
is not surprising if children return to poor, unsupportive, deprived environments. And, in
fact, such a finding supports the idea that IQ is malleable - in both directions.
New and better ways of educating, improving, and maximizing individual potentials in
intelligence are likely to be developed. As this happens, more and more of the
environmentally-influenced variation in IQ is likely to come under control and estimates
of the 'environment' proportion could increase.
Intelligence & occupation
"In more than 10,000 studies the average correlation of IQ with occupational
success was 0.3...this correlation is certainly a low estimate of its true
size...no other variable, either of ability or personality, can approach this
figure."
- Kline (1991), p. 139
Herrstein and Murray estimate the relationship between IQ and occupation to be between
.2 and .6 (i.e. that IQ explains between 4% and 36% of the variations in occupation).
These correlations are slightly higher for skilled, professional jobs, and slightly lower for
jobs that require less skill. Whilst this might be useful in describing groups, it means
there is questionable value in administering an IQ test to an individual in an attempt to
help determine their occupational options. It may be a useful approach, however, to help
select the best 100 employees from a 1000 applicants (Howe,1997, p.97).
Comments on the scope & quality of intelligence research
All this research uses psychometric, quantitative tests of intelligence, which we know
from previous lectures corresponds somewhat (but not entirely) with our conceptions of
what intelligence is.
The research is very focused on North American populations.
Multiple intelligences or subcomponents of intelligence are barely considered in much of
this research. Neither are alternative measures of intelligence, such as speed of
processing, evoked potentials, or practical intelligence, etc.
Future research on brain-behaviour connections will probably help to more accurately
isolate the functions of 'intelligence' (Weinberg, 1989).
In addition, as we come to understand and develop more effective environmental
interventions to maximise individuals' IQs, this will possibly expand the relative
important of the 'nurture' component.
Nevertheless, there remains the spectre of eugenics - those who would argue for selective
breeding on the basis of intellectual ability. This issue is likely to rear its head again in
the future and with new genetic technologies could appear in a more dynamic form.
The role of interaction"
An underresearched area, while the nature vs. nurture debate has raged, is the
contribution of interactions between genetics and environment on IQ variance.
In the overfocus on nature vs. nurture issues, the attempts to estimate the relative
contribution rests on the somewhat naive notion that there is a constant, true value. In
reality, "gene expression is environment dependent" and it impossible to obtain pure
estimates of genetic vs. environmental contribution - one could not exist without the
other.
The environment a child experiences is partly a consequence of the child's genes as well
as external factors. To some extent a person seeks out and creates his or her environment.
If she is of a mechanical bent she practices mechanical skills; if a bookworm, she seeks
out books. Thus genes may create an appetite rather than an aptitude. Remember that the
high heritability of short-sightedness is accounted for not just by the heritability of a gene
for short sightedness but by the heritability of literate habits.
Thus, a future area for research which blends those in the nature camps with those in the
nurture camps would be examine which environmental components allow people to
optimally realise their genetic potentials for a variety of areas of cognitive performance
(e.g. see Feldman, 1986).
What have we learnt about intelligence?
So, what can we say about nature vs. nurture as causal determinants of intelligence?
A conservative, seemly safe position is that:
"In the field of intelligence, there are three facts about the transmission of intelligence
that virtually everyone seems to accept:
1. Both heredity and environment contribute to intelligence.
2. Heredity and environment interact in various ways.
3. Extremely poor as well as highly enriched environments can interfere with the
realization of a person's intelligence, regardless of the person's heredity (Sternberg &
Grigorenko, 1997, p.xi).
4. Although most would accept a causal role of genetics, the exact genetic link and how it
operates is very far from being understood - another point that most psychologists would
agree on. It is certainly not a single gene, but a complex combination of smaller genetic
markers.
5. But likewise, it is difficult to pin-down single, identifiable elements of the
environment which directly influence IQ scores. Several environmental factors influence
intelligence.
So what have we learned about intelligence: that it's difficult to define but that there is
SOMETHING we call intelligence that appears to relate to ability to reason abstractly, to
learn and to adapt. That we can measure some part of it, although poorly; that it's
partially caused by genetics, partially be environment; that the real causes are the
complex, not well understood interplay between genetics and environment; that it is
somewhat though not greatly modifiable; that sometimes what we learn from tests is used
inappropriately but that IQ tests can be useful in helping children attain their potential.
Final quotes
"Measures of intelligence have reliable statistical relationships with important
social phenomena, but they are a limited tool for deciding what to make of
any given individual. Repeat it we must, for one of the problems of writing
about intelligence is how to remind readers often enough how little an IQ
score tells you about whether the human being next to you is someone whom
you will admire or cherish." Herrnstein and Murray (1994, p. 21)
"Mother Nature has plainly not entrusted the determination of our intellectual
capacities to the blind fate of a gene or genes; she gave us parents, learning,
language, culture and education to program ourselves with."
(Ridley, 1999, p. 77)
References
Anastasi, A., & Urbina, S. (1997). Psychological Testing (7th ed.). Upper Saddle River,
NJ: Prentice-Hall.
Bouchard, T. J., & Segal, N. L. (1985). Environment and IQ. In B.B. Wolman (Ed.).
Handbook of Intelligence: Theories, Measurements, and Applications (pp. 391-464).
New York: John Wiley.
Daniels, M., Devlin, B., & Roeder, K. (1997). Of genes and IQ. In B. Devlin, S. E.
Fienberg., & K. Roeder (pp. 45-70). Intelligence, Genes, and Success: Scientists respond
to The Bell Curve. New York: Springer.
Devlin, B., Fienberg, S. E., Resnick, D. P., & Roeder, K. (Eds.) (1997). Intelligence,
Genes, and Success: Scientists respond to The Bell Curve. New York: Springer.
Eysenck, H. (1971). Race, Intelligence and Education. London: Maurice Temple Smith.
Feldman, D. H. (1985). Nature's Gambit: Child Prodigies and the Development of
Human Potential. New York: Basic Books.
Gottfredson, L. S. (1997). Mainstream science on intelligence: An editorial with 52
signatories, history, and bibliography. Intelligence, 24, 13-23.
Herrnstein, R. J., & Murray, C. (1994). The bell curve. New York: The Free Press.
Howe, M. J. A. (1997). IQ in Question: The truth about intelligence. London: Sage.
Jensen, A. R. (1969). How much can we boost IQ and scholastic achievement? Harvard
Educational Review, 39, 1-123.
Kline, P. (1991). Intelligence: The Psychometric View. London: Routledge.
Liungman, C.G. (1975). What is IQ? Intelligence, Heredity and Environment. London:
Gordon Cremonesi.
Manolakes, L. A. (1997). Cognitive Ability, Environmental Factors, and Crime:
Predicting Frequent Criminal Activity. In B. Devlin, S.E. Fienberg., & K. Roeder (pp.
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