8/4/2019 Notes on Twins Studies

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Genes or environment ? Researching genetic influences on behaviour.

Since the 1970’ and 1980’s psychology has increasingly sought to find a genetic basis for behaviour and a new research subfield - Behavioural genetics has mushroomed. Behaviouralgenetics is the study of how genetic & environmental factors influence the behavioral differenceswe see between people - differences such as intelligence, depression, schizophrenia, personalitytypes, abilities and a whole host of other behaviours. This has come to be known as the nature –nurture debate. Although we won’t be studying genes, environmental or genetic influenceson behaviour as such the syllabus requires knowledge of the following;

• How we research genetic influences (physiological psychology research methods)

• The implications of genetic research (physiological psychology contemporary debate)

Background (we’ll take the example of intelligence )

Sir Francis Galton (cousin of Charles Darwin) was interested in the way that intelligent parentstend to have intelligent children. He assumed therefore that intelligence was inherited. But Galtonmay not necessarily have been correct in thinking that family intelligence was inherited. Heoverlooked environmental factors – for example parents who have a good education and aregenerally considered ‘intelligent’ may provide rich environments for the child to grow up in – suchas books, educational toys and other opportunities for stimulation. It’s more likely that there areboth genetic and environmental influences on our individual levels of cognitive ability.

Traditionally behavioural geneticists have investigated the role of genes and environment by threemethods; family studies, twin studies and adoption studies.You should be able to describe andevaluate each of these methods.

Family Studies

Children share 50 percent of their genes with each parent.Therefore, for genes to be influential whatsoever, the trait inquestion must run in families. Intelligence, for example is known torun in families. In fact Family studies of behavioural characteristicssuch as IQ test scores have consistently shown that familymembers are more similar to each other than unrelatedindividuals. However that trait could be environmentallytransmitted rather than inherited. Thus, findings from familystudies alone do not provide conclusive evidence of a geneticcontribution. Twin and adoption studies allow us to disentangle, to

some extent, the effects of genes and shared environmental factors

Adoption studies

Superior to family studies are adoption studies, which measure the correlation (relationship)between adopted children and their biological parents and between those same adopted childrenand their adoptive parents. As adopted children are raised apart from their biological parents anysimilarities must be due to genes.Can you think of any problems with adoption studies ?

8/4/2019 Notes on Twins Studies

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Studies of identical twins (raised together and apart)

Perhaps the best method is to study identical twins. Twin studiestake advantage of the fact that we know identical twins aregenetically identical. Logic tells us therefore that any differences inintelligence must be environmental in origin, and any similarities

must be genetic in origin. Research on a variety of traitsconsistently finds higher positive correlations between identicaltwins (MZ) compared to (DZ) twins raised together. Yet there stillmight be an environmental explanation for this. Perhaps identicaltwins become more psychologically similar because they aretreated more alike than fraternal twins.

Insert table here – jarvis p.149

Identical twins separated at birth provide us with a naturally occuring experimental condition of shared genes and a different environment. If separated identical twins have similar IQ’s in spite of different environments then this is powerful evidence for a role of genes in the devlopment of cognitive ability.

This has been supported by a widely publicized study conducted at the University of Minnesota, a

20 year study that began in 1979. The study tracked down separated twins from across the worldand subjected them to a battery of intelligence and personality tests. The similarities they foundwere uncanny. The video discusses the findings of this study.

Molecular geneticsAnother exciting direction in which behavioural genetics research has moved in the 1990’s is towardresearch in molecular genetics. Technological advances have allowed us to begin to extract genes fpeople, and to identify certain genes that seem likely to affect specific physiological or psychologica

characteristics. The easiest way to establish that a particular genemay be implicated in affecting a characteritic is to look at whether peop

who exhibit that characteristic are more likely to have the gene.

However such advances in molecular genetic research havemassive ethical implications. This is the contemporary debate w

shall look at in physiological psychology.