Nature vs. nurture

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Genetic Basis of Intelligence
Is intelligence determined by nature or nurture? Over the past few decades scientists and
psychologists have studied whether genes play a considerable role in determining our
intelligence. Schools and IQ tests concentrate on analytic problems in defining intelligence.
The actual effect of genes on IQ have not been proven but some of the answers proposed
are thatgenes can influence processing speed, ability to concentrate, motivations behind
learning and resistance to disease of the brain.
An experiment was carried out to investigate whether IQ is inherited or influenced by the
environment we are brought up in. The experiment was initially trying to prove the
hypothesis that IQ is determined by the environment and not genes. However the findings ofthe experiment showed otherwise. Thomas Bouchard of the University of Minnesota
collected pairs of twins who were separated at birth and reunited them to test their
personalities and IQs. Other studies compared the IQ of adopted children with their adoptive
parents as well as their biological parents.
Some key findings of the experiment are:
1)The percentage correlation of the IQ of identicaltwins living together is 86. However the
percentage correlation shown between fraternal twins was 55. Parents and children living
together show a percentage correlation of 40,
2) Biological siblings living together were 47 while adoptive siblings living together show zero
correlation.
3) For identical twins and biological parents and children living apart, the percentage
correlation islower for each group compared to the corresponding group living together.
These results provide evidence that there is a genetic basis behind intelligence as identical
twins show the highest percentage correlation of IQ compared to fraternal twins and
biological siblings. Identical twins share the same genetic composition and show more
similar IQ compared to fraternal twins who are geneticallydifferent but share their mother’s
womb. Ordinary siblings are genetically similar as they share the same parents but show a
lower correlation compared to twins. And to confirm this hypothesis, we see no correlation
between adoptive siblings growing up in the same household, so being in the same family
has no discernible effect on IQ at all.
However the results also show that intelligence is notentirely genetic, as we do not see a
100 percent correlation. About a fifth of one’s IQ depends on the environment, peer
influence etc. A task force of the American Psychology Association came up with the
average heritability of IQ of 50%.
There were further studies carried out to determine the actual gene that differed between
people who scored higher in intelligence tests compared toaverage people. Robert Plomin
from the Institute of Psychiatry in London found that a link exists between a specific gene
and high intelligence. A DNA marker introduced into the gene for insulin like growth factor-2
receptor (IGF2R) on chromosome 6 showed that a variant of the gene appeared more often
among 51 high intelligence children that among 51 children with more average abilities. This
isnot the only aspect of our biology that can affect intelligence. Robert J. Sternberg of Yale
University adds to the complexity: the IGF2R gene may influence intelligence in conjunction

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with other genes or specific environments. These other studies provide more evidence to
support the link between human biology and intelligence.
Evaluation of Research
There have been arguments aboutthe actual environmental difference in separated twins.
There is a possibility that the similarities are due to similar environments as opposed to
genes. It was found that separated twins are actually brought up in very similar
environments. Also, adoption agencies tend to use selective placement when assigning
homes to children. In other words they are placed into a family similar to their...
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