Top Ten Replicated Findings from Behavioural Genetics
Plomin et al (2016)wrote a ground-breaking article about Behavioural Genetics – but it is a little difficult to read, so I am
DNA by Naomi, cc licensed at Flickr
summarising it here, for those of you who might like to add it to your arguments regarding inheritance and IQ or mental disorders, or to present an argument outlining genetic predisposition and environmental stressors.
All of the findings briefly described have been successfully replicated many times, and some are now accepted as “laws” of behavioural genetics. Of course, as a famous behavioural geneticist, Plomin is bound to take this view, but he is backed up by a lot of science, as you will see below.
Finding 1. All psychological traits show significant and substantial genetic influence
Studies have shown thatnot just IQ, schizophrenia and depression, but also autism, substance abuse, drug dependence, personality and many others have a significant genetic component. (References in original article linked above). Genome-wide complex trait analysis (GCTA) uses hundreds of thousands of DNA differences across the genome to estimate chance genetic similarity for each pair of individuals in a large sample of unrelated individuals and to relate this chance genetic similarity to phenotypic similarity.
Finding 2. No traits are 100% inheritable.
While some traits, such as individual differences in height, yield a heritability of about 90%, there is nothing which is 100% inheritable. There is always an environmental influence.
Finding 3. Heritability is caused by many genes of small effect.
Genome-wide association (GWA) has been used widely in attempts to identify specific DNA associations with traits and disorders. An association is a correlation between a trait or disorder and the frequency of one of the two alleles (forms) of an single nucleotide polymorphism (SNP). For example, the frequency of a particular allele of the gene that encodes apolipoprotein E is about 40% for individuals with Alzheimer’s disease and 15% for control individuals who do not have the disorder. (See Caspi et al, 2003, for research into a polymorphism on the HRRT serotonin transporter gene and depression).
So it is a combination of many genes of small effect that result in the heritability of a trait.
Finding 4. Phenotypic correlations between psychological traits show significant and substantial genetic mediation
There is significant genetic overlap between anxiety and depression, and even between schizophrenia and bipolar disorder. Genetically, anxiety and depression are the same disorder. There is evidence for shared genetic risk between many disorders, and the genetic structure of mental disorders does not map neatly onto the DSM.
Finding 5. The heritability of intelligence increases throughout development
This is surprising, as if anything we would expect the environmental influences on intelligence to increase as we grew older. This could be due to new genetic influences, called innovation, as the brain structure changes throughout development.
Finding 6. Age-to-age stability is mainly due to genetics.
Phenotype stability from age to age is mainly due to genetics for personality, psychopathology and intelligence, for which most data is available.
This raises the question about the heritability of intelligence increasing throughout one’s life. It seems that genetic amplification might be responsible (rather than the innovation suggested above): genetic nudges early in development are amplified as children select, modify and create environments correlated with their genetic predispositions.
Finding 7: Most measures of the ‘environment’ show significant genetic influence.
Parenting, social support and life events show genetic influence, as humans select, modify and create environments correlated with their genetic predispositions regarding personality and psychopathology. How does this work? Well, parenting, for example, shows genetic influence that is driven by both child and parent inherited characteristics.
Finding 8. Most associations between environmental measures and psychological traits are significantly mediated genetically.
For example, there is a genetic influence on family socio-economic status (SES) and its association with children’s intelligence and educational performance. This is less surprising that it at first appears, as family SES correlates with parental intelligence. (This is a little worrying, as the risk is now that poverty will be seen as due to individual inheritance and therefore not needing social intervention.)
Finding 9. Most environmental effects are not shared by children growing up in the same family.
It is mainly genetics that accounts for similarity among siblings. It is not that the environment is unimportant, but that the relevant experiences are specific to each child in the family.
Finding 10. Abnormal is normal.
Common mental disorders are not qualitatively different from the normal range of behaviour; they are just extremes of the normal range. Genetic liability for disorders is distributed normally, and it is at the extremes of the same genetic influences that the common disorders occur. This has the possibility of opening up positive genetics for those in the positive area of the genetic liability (at very small risk) – looking at how these children and adults flourish and have resilience.
Some of this is a little scary, and it seems reductionist. The findings themselves fascinate me. But I hope they are not used to justify inequalities of opportunity.
After looking at some HL submissions for the Week 38 assignment on Aims and Procedure, it is clear that there is some significant uncertainty about precisely what a research hypothesis and null hypothesis entail. So I want to try in this short post to describe as precisely as I can what is and is not an acceptable hypothesis.
A research hypothesis is a prediction of the relationship between specific operationalized variables. It is NOT a conclusion about what has already been found, but a prediction of what will be found when the experiment is conducted. So a hypothesis should be framed in the future tense, not the present or past.
The best way to understand this is to look at an example with which you are all familiar: the Loftus and Palmer experiment on the effect of post-event information on memory. The conclusion to this study is clearly stated in the Abstract: These results are consistent with the view that the questions asked subsequent to an event can cause a reconstruction in one’s memory of that event. But what was the actual hypothesis being tested in this experiment? What were the IV and DV? The research hypothesis must explicitly mention which variables are actually being tested. So a statement like: The specific questions asked about the car accident changed the eyewitness’s memory of the event is not a research hypothesis. Neither the IV (the changed verb) nor the DV (estimate of speed) has been identified, so no specific prediction about their relationship has been attempted.
It is important to remember that the purpose of an experiment is to identify a cause-effect relationship between variables. The IV must be manipulated, and the DV must be measurable. In the hypothesis, both the manipulated and the measured variable must be clearly identified and operationalized. In Loftus and Palmer, the 5 conditions of the verb are the IV; the DV is the estimate of speed in mph. So the research hypothesis could take two forms. In a 2-tailed hypothesis: The changed verb will result in a change in speed estimate; in a 1-tailed hypothesis: The more emphatic the verb, the higher will be the speed estimate. Note that both forms are in the future tense: They are predictions, not conclusions!
A sound understanding of the research hypothesis should make the nature of the null hypothesis obvious. The null hypothesis is a statement that there will be no effect of manipulating the independent variable, and that any observed difference will be the result of chance.. It must still be framed in terms of the operationalized variables (like the research hypothesis, the null hypothesis must identify the IV and DV in an operationalized form), and should still be in the future tense.
When the experiment has been conducted, and the inferential statistic applied to the data, the null hypothesis can be either retained (accepted) or refuted (rejected).
Concentrate now on getting your hypotheses correctly constructed so that it is transparently clear to the examiner precisely what it is you think you are doing!
Pamoja HL students will soon be commencing their study of the Human Relationships option. Usually we start by looking at altruism, and the ‘bystander effect’ as it applies to the murder in New York of a woman called Kitty Genovese.
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This excellent article was published in the Guardian newspaper during the week that her killer died in prison. It exposes the mis-reporting, but maintains that the bystander effect, as tested by social psychologists, is a real phenomenon, and gives more up-to-date examples.
The bystander effect can also serve as a good example of how situational factors affect behaviour, and is an example that can be used by both HL and SL students. The presence of others and ambiguity of a situation can lead us to inaction when we would never have expected it of ourselves.
Every IB psychology student must submit one simple experimental study as part of the requirements for the course. This is marked by your teacher and moderated externally. The basic brief is that you need to plan and carry out a replication or slight modification (for HL) of a previous piece of psychological research. You then get to analyse your data and write up a report. This is really exciting and one of the most enjoyable parts of the course. K.I.S.S.
The biggest tip that I can suggest is to follow the KISS principle and ‘Keep It Simple Silly’! You only have 2,000 words to write up your report, and while that may seem like a lot at this moment, you will see it is really difficult to adhere to the word limit, and it is near impossible if you over complicate things. So, pick a simple study and make a direct replication or a small modification and you will be well positioned.
There is no place in the marking criteria for earning marks because you made it really hard on yourself. In addition, the requirements of the task are a replication or minor modification – so you cannot get too creative.
You have all been provided with the list of ‘safe’ studies for you to replicate. You need to select one from that list. We asking you to select one of these studies – this is because they offer you the best chance of success and also because you are ensured to be conducting an ethical study that you will be able to run in your school without the support of a face-to-face teacher. Ethics
There are clear ethical guidelines that are set out by the IBO for you to follow. There may be additional ethical considerations that your school or society also require you to adhere to. The ethical guidelines can be clearly read through on page 41 of the IB Psych guide. If you don’t follow the ethical guidelines you may be awarded a zero score – so it is very important that the study is ethically sound. One true study
You need to carry out an experiment that involves the true manipulation of an independent variable. By ‘one’, I mean, you have only one independent variable that has two levels. For example, if you were looking at a study like Loftus and Palmer (1975) – who had 5 levels of the IV (‘contacted’, ‘hit’ ‘bumped’ ‘collided’ and ‘smashed into’). You ONLY look at TWO of those verbs.
By ‘true’ I mean you need to ensure you avoid quasi-experimental variables. So you cannot use a pre-existing one like age, gender, handedness, culture or language. It must be clear in your report that you have manipulated a variable and have not just allocated participants to conditions because they are of a certain gender or age. For example, if you were looking to modify Stroop’s (1935) research by using ‘age’ by putting young kids in one condition and older kids in another condition, then you would NOT be running a ‘true’ experiment. This is because you have used a quasi-experimental variable.
Now that HL students have completed their formal study of Abnormal Psychology, it might be a good time to think again about how what you have learned can be applied to a better understanding of how things work in the real world. Our examination of psychological problems focused on the diagnosis and treatment of 3 common disorders: bulimia, depression, and PTSD. As part of your brief introduction to this hugely complex topic, you were asked to evaluate the three analytical approaches to these illnesses employed by psychologists and psychiatrists: the biomedical, the cognitive, and the socio-cultural. So this article on the increasing prevalence of PTSD amongst young women in England should raise important questions about which of these approaches seems the most appropriate, given the very particular parameters described in this study.
Note especially the recency of the upsurge, and its significantly greater prevalence in only one gender category. Can biology possibly provide an explanation for these statistics? The discussion of possible causes is fascinating, and should be of considerable interest to an audience very similar to the target population of the research.
For a more intensive expedition into critical thinking, this recent intervention should provide ample incentive. It’s not easy to follow the dense line of argument, but you might remember back to an earlier post about the perils of reliability in psychological research. This methodological issue matters a lot, and the fact that we insist so strongly that you must provide empirical support for all your truth claims should make it matter at a more personal, as well as theoretical, level.
As you begin serious engagement with your IA projects, you probably don’t need to dwell on the uncertainties of psychological research. But critical thinking is never out of place, and will need to be refreshed periodically as the Trial Exam and final IB Exam approach.
Welcome to all new Pamoja Psychology students, and welcome back to our Y2 students after the looong summer break! Courses start this week, and I was puzzling what I could write for this blog. My brain seemed to have turned to mush in the hot weather. Then I saw this article in the Guardian education section investigating whether being amibidextrous (using both hands equally for writing, bowling a ball, eating with a spoon, etc.) could boost your brain power. I am not – but am willing to give it a try if it helps. In fact, I am willing to try (almost) anything to boost my brain power at the moment.
However, unfortunately, it seems that this is not so. There is a certain logic to the idea: Most of us are right-handed, which means that the left side of the brain controls the fine motor movements in our right hand. The left side of the brain also controls the language centres in most people, and so is seen as the dominant hemisphere. So those of us who are right-handed at least could be forgiven for thinking that developing the use of our other hand to the same level would further develop our right brain hemisphere which seems a little neglected. This, of course, relates to brain plasticity. However, even if a certain activity is being mainly controlled by one or other brain hemispheres, the other side is still engaged; it is not inactive.
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The results of a study by Crowe et al (1998) suggest that being ambidextrous might actually be associated with cognitive difficulties. The Guardian article quotes cognitive scientist Michael Corballis, of the University of Auckland, who has conducted several studies into ambidexterity and academic performance. “The two hemispheres of the brain are not interchangeable. These asymmetries probably evolved to allow the two sides of the brain to specialise. To attempt to undo or tamper with this efficient set-up may invite psychological problems.”
So, I shall continue to pick up my coffee cup with my right hand – for now at least. And as for boosting my brain power, well I could do worse than read through the excellent advice given in some of these blog posts. I suggest maybe you do the same, and ease yourself into the year. Good luck! Keep in touch with your teacher and colleagues, and use the Help Forums in your learning space if you have questions.
As recently as 2014, Elizabeth Loftus wrote that as well as being easily created, false memories could also last a long time. However, the latest research questions whether false memories are indeed as easy to induce as psychologists like Loftus would have us believe. Brewin and Andrews conducted a meta-analysis of the research literature on false memories and concluded that “susceptibility to false memories of childhood events appears more limited than has been suggested.”
Brewin and Andrews are cautious in their conclusions, suggesting that even though susceptibility to false memories seems lower than previously suggested and therefore false memories themselves less common. Nonetheless, this has huge implications for the repressed memories of abuse that were claimed in court to be false memories. It is just one more example of how psychological thought is always advancing.
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