Genetics of Intelligence
Summary
According to this “Genetics of Intelligence” article, 52 researchers defined intelligence
as “a very general mental capability that, among other things, involved the ability to reason,
plan, solve problems, think abstractly, comprehend complex ideas, learn quickly and learn from
experience. It is not merely book learning, a narrow academic skill, or test-taking smarts.
Rather, it reflects a broader and deep capability for comprehending our surroundings –
‘catching on”, “making sense’ of things, or ‘figuring out’ what to do.” (Genetics of intelligence:
Deary, Spinath, Bates) With this definition in place, the question was whether outside forces
had more of an impact on intelligence or if it was majorly genetic make up. This idea of nature
vs. nurture drove this whole article and the tests incorporated in it. As far as nurture is
concerned, circumstances like income, place of birth, and family were considered. Natural
characteristics like brain size, birth weight, height and age were considered on the gene side.
Many tests are recording in this article but only a couple will be summarized.
One of the main tests performed and analyzed in this article is the Wechsler Adult
Intelligence Scale III. This scale is based on 4 different tests that are designed to influence
different parts of general intelligence: verbal comprehension, processing speed, perceptual
organization and working memory. Thousands of adults were brought in to take these tests
from different backgrounds and variations: poor and rich, short and tall, high education to low
education, black and white etc. This test was provided to see the correlation in scores between
people of specific differences.
To test the idea of intelligence being a heritable attribute more than a result of
environmental effect, the “Dutch Twin Study” was analyzed and considering. In this study about
194 pairs of twins were given tests geared towards non-verbal reasoning. These twins were all
the same sex and had the exact same gene make up. This study was then compared to the
Wechsler Adult Intelligence Scale III, seeing the test scores of twins to adults of different
genetic codes.
The WAIS was given to a group of 2450 adults and according to the article, people who
did well on a single subtest usually did well on the others. If a person did well on the test that
tested working memory, they tended to do pretty well on the other tests. A factor discovered
by Charles Spearman in 1904 shows that humans generally have a similar “general intelligence”
where any sample of humans have an average amount of cognitive intelligence. The majority of
humans get within a certain range of scores which shows a correlation between general
intelligence and the entire population. In the study, the range was about 0.26-0.77. This
suggests that intelligence is partially heritable. In most circumstances, humans will have a
certain degree of intelligence similar to others. These levels of intelligence were proved to have
correlation in the Dutch Twin Study with people who have similar gene make up. Twins tested
in 3rd grade 6th grade and up to adulthood, showed a correlation in the level of intelligence they
were capable of. They also found that some of the effects of genes were the specific areas of
intelligence the WAIS tested: verbal, processing speed, perceptual, and working memory. They
found that the older twins got, the greater the change of genes contributing to intelligence. As
a result the authors concluded that “the factorial structure of the WAIS subtests is determined
by individual differences in genetic structure. The co-variation among the WAIS subtests and
the co-variation between the subtests and the Dutch Twin Study and Raven in our data are
predominantly influenced by a second-order genetic factor and thus strongly support the
notion of a biological basis of general intelligence.” (Genetics of intelligence: Deary, Spinath,
Bates)
Although the article speaks about several different ways in which the idea of nature and
nurture influence intelligence, as a conclusion there are correlations between genes and
intelligence but not enough to prove the idea. General intelligence is something that has not
been proven wrong, the idea that human beings by genetic make up have an average amount
of intelligence that is common throughout the entire population. But factors like education,
financial statues, homeland and family greatly influence the amount of intelligence a person
can possess. In the battle of nature vs. nurture, nature wins the battle often but nurture seems
to ultimately win the war.
Bibliography
Deary, Ian J., Frank M. Spinath, and Timothy C. Bates. "European Journal of Human Genetics - Genetics of Intelligence."
Nature Publishing Group : Science Journals, Jobs, and Information. European Journal of Human Genetics, 15 Dec.
2005. Web. 7 July 2011. <http://www.nature.com/ejhg/journal/v14/n6/full/5201588a.html>.