With reference to relevant research studies, to what extent does genetic inheritance influence behaviour? (2.8)
LAQ Thesis: This paper will address the extent to which genetic
inheritance influences behaviour, specifically intelligence,
homosexuality and depression, as demonstrated in Bouchard et al.,
Santtila et al. and Caspi et al.
Key Terminology:
SAQ Thesis: One behaviour influenced by genetic inheritance is
intelligence (or homosexuality or depression), as demonstrated in
Bouchard et al. (or Santtila et al. or Caspi et al.)
Example: Gene that controls for shyness
Bouchard et al -Minnesota Twin Study
Research Method: Surveys/Interviews
Aim: To investigate how much of intelligence is genetically
inherited.
Procedure:
-
Used monozygotic twins raised apart (MZA) and
compared them to monozygotic twins raised together
(MZT)
-
Mean age of participants was 41 years old
-
50 hours of testing and interviews was carried out
o
“WAIS” IQ test was given, and participants were
given personality tests, aptitude tests, and
occupational interest inventories
Findings:
-
Concordance rates of intelligence are as follows:
o
Same person tested twice: 87%
o
Monozygotic twins reared together: 86%
o
Monozygotic twins reared apart: 76%
o
Biological siblings reared together: 47%
Conclusions:
-
Concordance rates show that intelligence is genetically
inherited as above correlation was parents and twins
-
Determined a genetic heritability estimate of 70%, 30% of
intelligence being attributed to other factors (such as the
environment)
-
Finding indicate that IQ can be increased, as it would
occur due to environmental factors
Genetic Inheritance: Traits that have been
genetically transmitted from the parents to the
offspring
Monozygotic Twins: genetically identical because
they are formed from one fertile egg that splits into
2 (same gender, look very alike)
Dizygotic Twins: From 2 eggs, no more genetically
alike than other siblings (not necessarily same
gender - about 50 % of genes in common)
Concordance rates: The higher the genetic
relationship, the more similar individuals will be if
the trait is inherited.
For example, if IQ heritability is high, there should
be a strong correlation of the IQs between the
children and the parents.
Applications:
Provides insight into how genetics can
influence intelligence
Spurs further research into heritable vs.
environment traits with twin research
Evaluation:
Strengths:
Applications
Cross-culturally valid
Large sample size
Qualitative research (interviews) provides
in depth information of the twins
Focus on older aged participants, whereas
previous twin studies focused on
adolescents
Limitations:
Reductionist
Ethical concern in the way he reunited
twins
Scarr, Weinberg, and Horn: Found no
significant differences in IQ correlations
between natural and adopted children and
their parents. Adopted children were from
poor, low class while parents were
wealthy, middle class. ∴ genes can’t solely
determine intelligence
Wahlstein: found children transferred from
low-class homes to high socio-economic
homes increased IQ by 12-16 points. ∴
environment plays a large role in
determining intelligence
Santtila et al.
Caspi et al.
Research Method: Questionnaires
Research Method: Correlational
Aim: To investigate how genes plays a role in determining
homosexual response and the potential for homosexual
behaviour.
Aim: To investigate the role of 5-HTT gene in
depression after experiences of stressful experiences.
Procedure:
Enormous twin study in Finland using 6001 female and
3152 male twins and their siblings between the ages of
18 and 33
The researchers thought that the potential for
homosexual response should be investigated, not just
the rate of homosexual relations
Researchers asked twins to answer a questionnaire to
establish sexual orientation, based on frequency of
same-sex sexual contact during the preceding year
Participants were also asked to rate how likely it would
be for them to agree to engage in sexual behaviour with
a handsome person of the same sex that suggested it, if
nobody would know and it could be done on the
participant’s own terms
Findings:
Reported incidences of homosexual behaviour were
3.1% for men and 1.2 % for women, but the potential for
homosexual response was much larger, with 32.8% of
men and 65.4% of women, suggesting there was some
chance that they would agree in the situation described.
Conclusions:
Concordance rates showed that MZ twins were more
than twice as likely to answer the questions in the same
way
Suggests there are genetic factors in determining
homosexual behaviour (even when they accounted for
possible effects of
shared environment)
Previous research into homosexuality has probably too
narrowly defined homosexuality by focusing on overt
behaviour rather than the potential for it
Applications:
Provides insight into how genetics play a role in
homosexual and potential homosexual behaviour
Demonstrates how previous research had defined
homosexuality too narrowly
Evaluation:
Strengths:
- Applications
- Large sample size
- Takes environmental factors into account
Limitations
- Ethical concerns: socially sensitive issues
- Lack of cross cultural validity
- Reductionist
Procedure:
847 Caucasian New Zealanders were
participants in this study
5-HTT gene influences the level of serotonin,
which is known to play a role in controlling
mood
Researchers compared participants with a
normal 5-HTT gene and a mutation of the 5HTT gene with shorter alleles. Both types are
quite frequent in humans but the long allele is
slightly more frequent (57%)
Stressful events occurring after the 21st
birthday and before the 26th birthday were
assessed
Findings:
Researchers found that participants who
carried mutation of the 5-HTT gene (short
allele) and who had experienced many
stressful events were more likely to become
depressed after stressful events than those
participants who carried the normal 5-HTT
gene.
Conclusions:
5-HTT gene could indicate a vulnerability to
depression after stress and the researchers
speculated whether the gene could moderate
individual responses to environmental factors.
Applications:
Provides insight into how genetics can play a
role in depression
Provides basis for further studies on this topic
Evaluation:
Strengths:
Applications
Longitudinal study
Internal Validity
Weaknesses:
It can be difficult to conclude that the gene is
a major contribution to depression. People
who did not carry the mutation also became
depressed
Correlation between presence of the 5-HTT
short allele and depressions but no clear
cause and effect relationship
Genes contribute to some extent to behaviour
but there is no evidence against idea that
stressful events (environment) causes
depression
Ignores sociocultural factors
Reductionist