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BLoA Research Studies Summaries
IB Psychology
Mr. Detjen
BLoA Research Studies Student Summaries
Genetics and Behavior
Alyssa January
Bouchard et al. (1990): Minnesota Twin Study
The aim of the Minnesota Twin Study, Bouchard et al. (1990), was to investigate the role of genetics
and the environment on intelligence. This study was cross- cultural, correlational and longitudinal because it
was carried out over a period of time investigating the relationships between genetics and the environment on
intelligence. The study compared identical twins that were raised together and identical twins that were raised
apart. Each twin went through about 50 hours of interviews and examinations. The results yielded that 70% of
intelligence can be attributed to genetic s and the other 30 % to other factors. It can be concluded that both
genetics and the environment have an effect on intelligence. Strengths of this study include the cross-cultural
sample and the size of the study. Limitations of this study include the assumption that twins that were raised
together had an identical environment and the ethics of separated twins being reunited.
Thomas J. Bouchard, Jr., David T. Lykken, Matthew McGue, Nancy L. Segal, AukeTellegen
MZAs: Identical twins raised together
MZTs: Identical twins raised apart
Taylor Alexander
Learning Objective: With reference to relevant studies, to what extent does genetic inheritance influence
behavior (cognitions, emotions, behavior)?
In 1981 Bouchard TJ Jr. and McGue M. Familial conducted a meta-analysis study in which suggested that genetic
inheritance influences cognitive behavior. Using the meta-analysis methodology, the aim of the study was to investigate
the role of genetics and establish whether or not there are correlations between siblings. Meta-analysis is the statistical
amalgamation of data from similar, comparable studies of a problem that produces a range of results. Bouchard and
McGue reflected on 111 IQ correlational studies that focused on the correlation between IQ and siblings. After
calculating the mean correlation between monozygotic twins, half siblings, siblings, and cousins, Bouchard and McGue
found that there was a higher correlation for IQ for those of closer kinship.
Strengths of Bouchard and McGue’s study that makes it relevant to the learning objective are the use of
monozygotic twins, its validity, and generalization. The use of monozygotic twins enables scientist to judge
influences of behavior because of the twins’ 100% identical genetics. The study is valid due to its ability to be
replicated and, as a meta-analysis study, incorporated various studies with similar results; because the results
are common amongst various sets of monozygotic twins, the results can be generalized. One limitation could be
the use of studies that may have been bias. Another reason Bouchard and McGue study of 1981 could be a
relevant study to the learning objective is because it supports the suggestion that IQ is based on genetics more
so than environment.
Kaliice Walker
Horn et al. (1979)
The “Intellectual Resemblance Among Adoptive and Biological Relatives” was conducted in 1979 by,
Joseph M. Horn, John C. Loehiln, and Lee Willerman. It was apart of the Texas Adoption Project.
It was an experiment that aimed at determining the correlation between genetics and intelligence,
between children and their adoptive parents.
The study was conducted with 300 families. Researchers tested parents, their adoptive children and their
biological children using an IQ test.
They found that there were no significant differences in IQ correlations between parents/biological
children and parents/adoptive children. This experimental study implies that intelligence is based on
“nurture” rather than “nature”.
One limitation of this study is that its model assumes that adoptive and nonadoptive homes are
comparable in terms of means and environment. Another limitation was that the IQ’s were assessed of
children and the parents with two different IQ tests. Also the studies were done on very young children,
a follow up with the families 10 years later showed that most of the adoptees had little or no intellectual
resemblance to their adoptive parents or other siblings in the family.
Jarren Gorka
In 1966, Leonard Heston set out to find whether schizophrenia is an issue
of genetics. Through a longitudinal study of 49 adopted children whose
biological mothers were schizophrenic, Heston compared those findings to
other adoptees, living in the same household as those 49, whose biological
mothers did not suffer from schizophrenia.
The occurence of schizophrenia in the general population is around 1%.
Heston found that 16% of the adoptees, whose biological mothers were
schizophrenic, were later diagnosed with the same disease; however, none
of the adoptees involved in the study, whose mothers were free of
schizophrenia, were diagnosed with the disease later in life.
Heston’s findings seem quite reliable considering he observed two separate
groups of adoptees of varying family histories while taking into account
the issue of environment; however, his number of participants was
considerably low, which begs the question, can these findings really be
applied to a larger population?
Regardless, Heston’s research does in fact show a correlation between
genetic inheritance and schizophrenia.
Hannah Florence
Santtila et al. (2008): Finland twin study and homosexuality
The study titled “Potential for Homosexual Response is Prevalent and Genetic” (2008) was
researched/conduted by Pekka Santtila, Kenneth N. Sandnabba, Nicole Harlaar, Markus Varjonen, Katarina
Alanko, and Bettina von der Pahlen. The researched was conducted using a qualitative method and a
questionnaire. The aim of the research was to distinguish if homosexuality is genetic and can therefore be
inherited. These researchers wanted to evaluate the theory that homosexuality differs from reported rates to the
actual occurrence of homosexual attraction.
To gather the appropriate data, a large twin in Finland was conducted. The participant population
included 6001 females and 3252 males. The questionnaire asked the twins for their sexual orientation and how
likely they would be to involve themselves in sexual intercourse with someone who was of the same sex and
attractive if the opportunity presented itself and no one would know about it.
According to the questionnaire results, monozygotic (MZ) twins, males and females, showed
approximately a 53% and 52% chance for potential homosexual relations. Overt homosexual behavior, as
depicted by the questionnaire, showed, respectively, a 38% and 59.4% chance. Dizygotic (DZ) twins, males and
females, with potential homosexual behaviors showed about a 23.4% and 26.4% chance. Overt homosexual
behavior among DZ twins showed a 0% chance of occurring.
With relation to genetics, it can be seen that the concordance rates for both aspects of the questionnaire,
potential and overt homosexual behavior, indicate a genetic link due to the fact that MZ twins were over twice
as likely to answer each question the same.
Dominique Price (and Colin K.?)
Case Studies for Genetics and Behavior
Tetsuro Matsuzawa is a primatologist who used chimpanzee’s to study their aptitude in a number of
ways including but, not limited to: communication skills, number concepts, and memory ability. His main
subject that he used in his studies was a female chimpanzee name Ai; whom would be the case of Matsuzawa’s
studies for many years.
Matsuzawa was able to assess through data collected from testing Ai that chimpanzees are able to outperform
human beings in areas of memory such as numerical memory recollection.
In the actual study Matsuzawa required chimps and humans to memorize a the location of a numeral on
a screen and then map out where the numbers were after the screen was cleared. The test also, required that the
process of mapping out the location of the numerals be accomplished in numerical order. The results of the
study showed that not only did Ai have a higher percentage of correct trials in the test than the tested humans
but, that the chimp accomplished the task at a much faster rate. Thus, the theory that chimpanzees had a higher
aptitude in spatial memorization and recollection was dawned by Matsuzawa in his case study of 2007; however
it was quickly challenged and disproved in 2008 by Silberberg and Kearns.
Inoue Sana, Tetsuro Matsuzawa. “Working memory of numerals in chimpanzees”. Current Biology vol. 17 No.
Jolie Huynh
In 1977, Scarr and Weinberg conducted the Minnesota Adoption Studies aimed to find the environmental
impacts on black and interracial children adopted by white families based on their performance on IQ and
school achievement tests. The researchers hypothesized that black and interracial children adopted by white
families would perform just as well as white children from the same families. The sample of the study included
101 transracial adopted families, 176 adopted children, and 143 biological children of the adoptive parents.
Most of the adoptive children were adopted when they were around one year old. The researchers carried out
the study by giving IQ tests to the parents, their biological children, and their adoptive children. The results
showed that the adopted black children scored 20 points higher than children raised in black community and
had similar IQ scores to the adoptive parents and their non-related siblings. This led to the interpretation that
environmental factors rather than genetics play a large role in IQ performance.
Charles Burt
Kendler et al. (1991): Twin study and Bulimia Nervosa
The authors of the Kendler (1991) twin study are Kenneth Kendler, M.D., Charles MacLean, Ph.D.,
Ronald Kessler, Ph. D., Andrew Heath, D.Phil., and Lindon Eaves. D.Sc.. The official title of this study is: The
Genetic Epidemiology of Bulimia Nervosa and it was completed in 1991. The data was collected through a
series of interviews with 2,163 female twins. The aim of Kendler’s study was to discover whether or not the
eating disorder bulimia nervosa, is either genetic or environmental. The procedure of this study included
interviewing sets of twins and assessing their symptoms level of bulimia nervosa. They were also assessed on
their equal environment assumption to ascertain how similar the twin’s environment was while growing up.
After interviewing and evaluating the sets of twins that were identified as having bulimia nervosa, it was found
that in 22.9% of monozygotic twins had bulimia together and 8.7% of dizygotic twins experienced bulimia
together. Kendler concluded that there was a 55% chance that bulimia nervosa was inheritable and the other
45% could be contributed to environmental factors. A strength of this study is that strengthens the naturenurture theory that it is a combination of both and not just either/or. The study is limited in that it only provides
information for female twins. Bulimia nervosa is not a strictly female disease and these findings do not relate to
the male population. Female twins also do not necessarily represent the population as a whole. This study
relates to the BLoA in that it supports that human actions or experiences can be influenced by genetic factors.
Megan Ratcliff
Konrad Lorenz’s Imprinting Experiment
1) Konrad Lorenz, Imprinting, 1935/1937
2)Experiment. The aim of his experiments was to test his theory of imprinting. Imprinting is described as
involves a sensitive period during which the young animal must be exposed to a model, and the learning that
occurs at this time may not affect behaviour until some later date
3)Procedure: Lorenz divided a a clutch of eggs into two groups. ONe was hatched by the goose, the other by an
incubator. He then marked each of the ducklings so he could distinguish between the two groups and put all the
ducklings under a box. When he lifted the box, the ducklings went to each of their respective “parents”. He
called this phenomenon “Imprinting”
4)Results:The geese that were hatched by their mother, followed her upon first sight. The other group did not
see their mother, but saw Lorenz instead, so they followed him around. This led Lorenz to conclude that there is
a critical period of time in early life where specific stimuli must occur in order for normal development. He also
speculated that this stimuli would have a later effect on the sexual behavior of the animal.
5)Strengths: Lorenz was able to manipulate variables to support his theory.
Limitations: His experiments focused only on Geese and other birds on his farm in Austria. And while it is more
frequent in avian creatures,
Relevance: This study is relevant to genetics and learning because Lorenz showed that the Geese were
influenced by their first sight, and even though Lorenz was not the father of the Geese, they still flocked to him
as their parent because of imprinting. But, whatever Lorenz taught the geese, they applied to other members of
their species.