a) What is meant by ‘genetic influence’? (3)
OR What is meant by ‘environmental influence’? (3)
b) Critically consider the balance of genetic and environmental influences on human
behaviour (22)
Essay Plan for part b)
Introduction -This debate is of interest to psychologists because we are interested in the
extent to which our genes influence aspects of behaviour such as intelligence, mental illness
or personality for example. More recently it is widely accepted that an interaction of both
genes and environment influence human behaviour however prior to this biological
psychologists took a very reductionist view that genes may be a sole influence on behaviour
and behaviourists took an extreme view of environmental determinism. Hence this debate
was until recently often termed the nature vs nature or learned/innate debate.
AO1 The interaction of the environment with our genes can be shown through the recent
discovery of epigenetics and differences between genotypes and phenotypes. For example
identical twins with the same genetic make-up (geneotype) who are reared apart can end
up with different physical characterisitcs (phenotype) due to environmental factors such as
diet or pollution. These factors have the effect of switching on certain genes e.g which
govern height of a person, which may then be inherited by the next generation.
AO2 However it is also thought that our genes can affect our environments directly and
indirectly. For example Plomin et al (1977) suggested that infants can create
microenvironments based upon genetic tendencies such as aggression. Furthermore a
genetically determined mental disorder of a parent could affect the environment of a child
triggering the same disorder in the child. Scarr and McCartney (1983) suggest that genes
can influence what kinds of activities a child might prefer and therefore select as they get
older. Therefore they ‘niche pick’ and actively create their own environments based upon
genetic factors.
AO2 This explains why siblings who share 50% of their genes and the same environment do
not show high concordance rates on characteristics but it does not explain why identical
twins (MZ) do not show 100% concordance.
AO1 When looking for the extent of genetic and environmental influences on behaviour
biological psychologists have used twin studies or gene mapping to gather heritability
estimates for a certain characteristic such as suffering from Schizophrenia for example. This
is an estimate of the extent of a genetic cause which then also gives an indication of the
extent of environmental causes also. For example Chorney et al found specific genes
associated with high IQ.
AO2 However this is controversial as other studies such as Turkheimer et al suggest that
socio-economic status has a bearing on IQ which is an environmental factor.
AO2 This shows that environmental enrichment supplied by more ealthy parents has the
effect of ensuring that genetic IQ is maximised.
AO1 Twin and adoption studies suggest that heritability of mental disorders is high. For
example Joseph (2004) suggested concordance rates for MZ twins is 40% for schizophrenia.
AO2 However the Diathesis Stress Model shows that genetic predispositions towards the
illness are increased by environmental factors such as family conflict for example.
AO1 Behaviourists since the 1930s have suggested that most behaviour is due to
environmental factors such as reinforcement. For example Bandura’s classic bobo doll
study showed the effect of vicarious reinforcement on the aggression of children.
AO2 However Coccaro et al (1997) suggest 50% of variance in aggressive tendencies is due
to genes.
AO1 Further studies have shown the extent that our environments can affect our actual
biology. For example Blakemoor and Cooper (1970) raised kittens in an enclosure restricted
to either vertical or horizontal lines. After five months the kittens were unable to see lines
other then the ones they were exposed to meaning that their visual cortex had developed
differently as a consequence of their environment.
AO2 In support of this idea Maguire et al (2000) carried out brain scans on London Taxi
drivers and found enlarged hippocampi (responsible for long term memory) which he
suggested was due to learning London taxi routes (the knowledge).
Conclusion – Psychologists now widely agree that both genetic and environmental
influences on behaviour are entwined for the reasons discussed in this essay. However they
still debate the extent of these influences and research studies often contradict each other.
There is evidence of genetic involvement in intelligence and mental disorders but
environmental influences cannot be discounted. There is also evidence of environmental
influences on personality traits like aggression for example however the extent that these
are rooted in genetic differences is still unknown.