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With reference to relevant to research studies, to
what extent does genetic inheritance influence
behaviour.
Introduction

o
State what you are doing in the essay
This essay will attempt to consider the merits or otherwise of the influence
of genetic inheritance on behaviour.
o
Outline the overarching principle
According to the third principle of the biological level of analysis (BLA),
behaviour is innate and inherited

because it is genetically based (we are predisposed to a specific behaviour
due to genetics).
Describe genetics and the importance of research into genetics

It is argued that people have a genetic predisposition.
Genes are segments of DNA inherited by the offspring from the parent.
o
o
o
o
o
o
Genes are considered responsible for the development of behavioural
characteristics.
Behavioural Genetics is the understanding of how genetics and environment
contribute to individual variations
in human behaviour, where the premise is that the inheritance of DNA
influences behaviour.
It cannot be said that a single gene is responsible for a specific behaviour
– but it is a building block.
But genetics alone does not affect behaviour
 Environmental factors (e.g. culture, diet) also influence the development
of an organism.
o


Genes are complex
It is unlikely that a single gene is responsible for such complex behaviours
as schizophrenia or depression.
There is no causal relationship between a single gene and a specific
behaviour.
It is thought that what is inherited is the gene that can lead to the
development of the specific behaviour, not
o

the behaviour itself.
This means that an individual may have a genetic predisposition to a
behaviour but without appropriate
environmental stimuli, the behaviour will not be manifested
Don't forget to state that behaviour is bi-directional, explain.

Type of studies used in genetic research
Twin studies
 Used in genetic research to study the correlation between genetic
inheritance and behaviour due to the
o



common genetics shared by twins.
Monozygotic twins (MZT) identical - share 100% genetic material.
Dizygotic twins (DZT) fraternal - share 50% genetic material.
It is usually further explored, by studying the twins either separated or
together to make a correlation of
their behaviour.
Adoption studies
o


Allow researchers to study the comparison between genetic and environmental
influence on behaviour.
Adopted children share no genes with their adoptive parents but 50% of genes
with their biological parents.
Family studies
o
Study behaviour between family members who have similar genetics to different
degrees. Inheritance

Outline intelligence
o


Intelligence is an aspect of behaviour that has been studied in relation to
genetics.
It was questioned whether intelligence was attributed to genetic or
environmental factors. Intelligence is

difficult to define
IQ tests have been developed by a French person called Binet to measure of
intelligence and are used in
much psychological research.
Body
Introduce studies into genetics

Examples of studies into genetics include...
Study 1: Bouchard and McGue (1981)
Method:


Conducted a meta-analysis – statistical synthesis of data that yields a
quantitative summary of pooled results
Reviewed 111 studies of intelligence correlations between siblings.
Results:

The closer the kinship, the higher the correlation for IQ, which supports the
influence of genetics on intelligence.
Study 2: Bouchard et al. (1990) - Minnesota Twin Study
Aim:

To determine how much of intelligence is attributed to genetics and
environment.
Method:


Longitudinal study
Over 100 sets of MZT (monozygotic – identical twins raised together) and DZT
(dizygotic – fraternal twins raised

together) from around the world who were reared/raised together and apart.
Researchers gave them approximately 50 hours of psychological and
physiological testing.
Results:

Similarity rates between MZTs reared apart was approximately 76%

Bouchard determined a heritability estimate of 70% of intelligence attributed
to genetics, and 30% to other
factors.
Connection of study to question

This study relates to the effect of genetics on behaviour as the concordance
rate between twins shows that their
behaviour was affected mostly (70%) by genetics, rather than the environment,
where the other 30% may be
attributed to other factors in the surrounding environment.
Evaluation:

Strengths:
o much research has supported his findings, making them more reliable
o

large sample of participants, making the study more externally valid than
most twin studies
Limitations:
o
o
o
Bouchard used media coverage to recruit the sample
No control over the frequency of contact between twins before the study
Bouchard assumed that the twins reared together experienced the same
environment – equal environment
assumption
Study 3: Shields (1962)
Method:

Obtained 44 pairs of MZTs reared apart via the media
Results:




They had a similar 0.77 correlation in IQ.
This was very similar to that of MZTs reared together (0.76)
This means that the environment had very little influence on the twins?
intelligence.
DZTs reared together had a significantly lower similarity in IQ (0.51)
Connection of study to question

This study supports that genetic factors have a larger influence on behaviour
than environmental factors as the
MZTs reared apart had a higher similarity in IQ compared to the DZTs reared
together.
Evaluation:

Strengths:
o
o
o
o
Similar findings have also been found by other, better-controlled studies
o
This shows that genetics play a significant role in the similarity between
twins, thus supporting Shields?
findings.
Pederson et al. (1992) studied the aging of DZTs and MZTs in Sweden.
Half the twins were separated before the age of one.
It was found that MZTs reared together had a similarity rate of 0.80 and DZT
reared apart had a rate of
approximately 0.32.

Limitations:
o
Kamin (1977) argued that the MZTs spent a substantial amount of time
together, suggesting that their
environments were not completely different.

Environmental factors such as race have also been found to have an influence
on intelligence levels
Introduce adoption studies:
-In adoption studies, the intelligence of the adopted child is correlated
with the intelligence of the
adoptive parent.
-Since there is no biological link between the adoptive parent and the child,
the environmental
influence should be evident.
Study 4: Scarr and Weinberg (1976)
Assumptions, aims and introduction:


They focused on parents who had raised both natural and adopted children.

Any significant differences between parent-child IQ correlations for adopted
and natural children were attributed
to genes.
The assumption was that all children will have similar
behaviour/characteristics, having the same upbringing, and
being raised in the same environment, with the same parents.
Method:

Trans-racial adoption participants who were African American children adopted
by middle-class White families
Results:





The researchers found no significant difference in IQ correlations.
They were found to have an average IQ of 106 at the age of 7
Whereas children of a similar background brought up in low income biological
families had an average IQ of 97.
The IQs of the adopted African American children in Scarr and Weinberg’s
study was tested years later.
By age 17, their IQs had dropped to 97 – same as the average for children of
similar background brought up in
their biological families. (Weinberg et al., 1992)
Connection to study question




This finding supports the influence of the environment on behaviour,
overriding the influence of genetics.
This suggests that intelligence has a lot to do with the environment as well
as genetics.
Through this study, researchers have made a link that “an enriched
environment may raise IQ in children.?
However, it is also likely that there is a strong interaction between genes
and the environment to produce
intelligence level.
Evaluation:

Limitations:
o
IQ of parents was unknown

for.
No consideration of the selective placement of children
o


o

There may have been a correlation between the IQ of the parents and the
children which was unaccounted
Often adoption agencies attempt to place children into families that they are
similar to
This may be the cause of the concordance rate between the adopted children
and their adoptive family
Lack of consideration for children who were adopted at a late age and may
have been brought up in care
Weinberg et al.'s findings support the “niche picking? hypothesis proposed by
Scarr and McCartney (1983)
Genes affect an individual’s preference for particular environments
The environment then affects the development of the individual.
o
o
o
o
Genetically similar people will tend to select similar environments, thus
leading to similar IQ.
Supported by Plomin and Petrill (1997)
o
Found concordance rates of IQ between biological parent and child increase
over time
It is possible that genetic predisposition influences individuals to tend
towards environments that accentuate
o
that disposition, thus leading to increased heritability throughout their
lifespan.
The niche picking hypothesis supports the influence of genetics on IQ.

Conclusion


Genetics can influence intelligence as shown by supporting studies on
influence of genetics.
Scarr and Weinberg provided findings to suggest that the environmental factor
of race affects intelligence
o Adopted children have a higher IQ correlation with the race of the adoptive
family, rather than biological race.
o
o

o
o

However, upon later testing, the adopted children’s IQs correlated with that
of biologically similar children,
rather than adoptive race.
Explained by niche picking (Scarr and McCartney, 1983), which supports
genetic influence on intelligence.
Genetic inheritance influences intelligence, and thus behaviour, to a great
extent.
large amount of supporting research
the niche picking hypothesis refutes environmental factors
Although it is important to note that the role of genetics in determining
human behaviour and physical
characteristics is significant, it is essential to bear in mind that although
some characteristics are strongly affected
by genetic inheritance, it is not a simple causal relationship, as other
factors such as the environment can influence
thus alter certain behaviour.
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