2.2 Pysch Studies

Minnesota Twin Study – Bouchard et al. 1990
Aim – To identify how genetics and the environment influences intelligence of twins, and which plays a bigger role in the development of the intelligence in each twin.
Methods – The Minnesota Twin Study is a longitudinal study ongoing since 1979; MZA’s, or identical twins that are raised apart, are compared to MZT’s, or identical twins raised together; mean age of the MZA’s was 41 years old (at the start of the study); each twin completed approximately 50 hours of testing and interviews (to determine level of intelligence)
Results –
Same person tested twice
Identical twins reared together
Identical twins reared apart
Fraternal twins reared together
Biological siblings reared together
70% of intelligence can be attributed to genetic inheritance, leaving 30% to other factors, such as ‘nurture’, or environmental influence; these results support the idea that genetics may play a larger role than the environment in developing intelligence
*Mean age of MZA’s was 41, which provided a more unusual sample than the sample of adolescents which are used more conventionally in other twin research. However this is also a limitation.
Very cross-cultural, with participants from all over the world.
Size and nature of sample allows results to be generalized.
Relied on media coverage to recruit twins: essentially gives away his aim, and increases the chance his aim influences twin responses or interaction, nullifying the credibility of his results.
Ethical concerns about the way he reunited twins: traumatic experience.
No control to control and/or impede the interaction of twins prior to the study.
Equal Environment Assumption – all environments will be different in some way.
Ethical Considerations
Reuniting the twins can be seen as morally wrong, and a traumatic experience. (Protection from harm)

Scarr and Weinberg 1977
aim – determine the contribution of environmental factors vs. genetic factors on the differences of parent-child IQ correlations for white parents and their black adopted children and white natural children
method -adoption study; participants – parents who raised both adopted and natural children assumed to have been raised with the same upbringing; adoptive parents were wealthy, white, and middle class with high IQs; adopted children were from black kids from poor, lower class backgrounds with low IQ parents
results – no significant difference in IQ correlations, so this suggests that the environment has more of an effect on intelligence than genetics do
strengths – the adopted kids went from a background of low IQs to a background of high IQs so the results show that the change in IQs surrounding the children helped to change their IQs
limitations -the adoptive parents were all mostly wealthy, white and middle class so they are not a good representation of all of the human population

Wahlstein 1997
aim – to see if changing the environment would affect an adopted child’s IQ
methods – infants were transferred from a family with a low socio-economic status to a family with a high socio-economic status
results – their childhood IQs improved by 12-16 points, which suggests that the environment has a large effect on intelligence, as well as genetics
limitations – no sample size given; no information about a control group; no age of the participants given

Matsuzawa 2007
Aim: To examine spatial memory in young chimpanzees
Methods: Three pairs of chimps and three pairs of humans were taught to recognize the numerals 1-9 on a computer monitor in a random sequence. The numbers were then replaced with blank squares. Participants had to remember which number appeared in which location and touch the squares in the appropriate sequence.
Results: The humans did worse as the test sped up. The chimps made few errors and speed did not affect their memory. This shows that it is a necessary adaptation for chimps to have this type of memory so that they can remember where food resources and dangers are in the rainforest, and as agriculture developed this skill was no longer essential for human survival. Chimps and humans have adapted to become most suitable for the respective environments in which they live.
Strengths: Strong evidence for evolutionary adaptation
Limitations: Lacks ecological validity

Fessler 2006
Aim: to see if the emotion of disgust allowed our ancestors to survive long enough to produce offspring, who pass the same sensitivities on to the offspring. Hypothesis: that the nausea response helps to compensate for the suppressed immune system
Method: He investigated the nausea experienced by women in their first trimester of pregnancy. During this period of time, hormones are infused to lower the expectant mother’s immune system so as not to fight the new foreign genetic material in her womb. He had 496 healthy pregnant women between the ages of 18-50, and asked them to consider 32 potentially “stomach turning” scenarios (ex. walking barefoot and stepping on an earth worm, someone accidentally sticking a fish hook through their finger, and maggots on a piece of meat in an outdoor waste bin.) Before asking the women to rank the scenarios based on how disgusting they were, Fessler posed a few questions, designed to determine whether they were experiencing morning sickness.
Result: Women in their first trimester scored much higher in disgust sensitivity than the women in their second and third trimester. When Fessler controlled the study for morning sickness, the response only held for disgusting scenarios involving food. h(ex. maggots on meat). This shows that natural selection helped to compensate for the increased susceptibility to disease during this risky period in pregnancy by increasing the urge to be picky about food. Disgust is a form of protection against disease.
Strengths: evidence of evolutionary psychology, large amount of participants

Hutchings and Mednick 1975
Aim: To investigate to what extent to which genetics play a role on the genetic basis of criminality through adoption studies.
Method: Research was carried out through adoption studies
Results: They found that if both biological and adoptive fathers had criminal records then 36.2% of sons also had a criminal record. If only the biological father had a criminal record then 21.4% of sons had a criminal record. If only the adoptive father had a criminal record then 11.5% of sons had a criminal record.
Limitations: Children are often placed in a similar environment to their environment before adoption. Some children are adopted years after birth causing early experience with biological family to have contributed to later behavior. Crime is also a broad term from murder to shoplifting and their is no gene specifically for crime. Genetic theorists have a difficult time explaining why criminal behavior changes over a lifetime (peaking in ones’ 20’s and declining by their 30’s).
* Showed that environmental factors and genetic factors have roles in determining behavior.