Unit 9, Lesson 9.3, Exercise C≤2.13
Part 3 Now, let’s look at the last point on our slide: genes and the environment. The question is … is personality inherited or environmentally determined?
The theory that personality is based on brain
structure has a long history, and until recently, not much of it was scientific. However, the extraordinary case of Phineas Gage, that’s G-A-G-E, does illustrate the influence of different parts of the brain on behaviour. In 1848, Phineas Gage suffered an accident in which an iron rod went through his cheek and the frontal lobe of his brain. Amazingly, he survived the accident, but changed from being a serious, reliable person to being irresponsible and reckless. In effect, brain damage had altered his personality. This is fairly strong evidence that behaviour is dependent on specific parts of the brain. You can find a full account of the case in Personality: theory and research by Pervin (the 9th edition was published in 2005) … it’s in the library.
If we accept, then, that personality is in some
ways determined by our physiology, which is inherited from our parents, then it would be logical to assume that our personalities are also inherited, wouldn’t it? So how do theorists prove this? Well, the most common method for investigating genetically-inherited characteristics is carrying out ‘twin studies’ … with identical (or monozygotic) and fraternal (dizygotic) twins.
If we want to look at this in a bit more detail we
can to go back to trait theory. There are trait theorists who take the view that the Big Five personality traits are inherited. In your core text, Psychology (the 6th
edition was published in 2003),
Gleitman reports Borkenau’s study of German adult twins, from the Journal of Personality and Social Psychology, 2001, which showed a 40–60% correlation between the behaviour of identical twins, in comparison with a 20–30% correlation for fraternal twins. Quite convincing evidence, I think.
By the way, I see that some of you are using the
Cornell note-taking system. That’s very good. Do you all know about this? No? Right, well, if you want to know more about it, I suggest you look at How to study in college by Walter Pauk, the 9th edition, published in 2007. It’s very good, and it should be in the university library. I’m sure that you all know the importance of taking good notes – and this system is particularly useful.
Anyway, getting back to the point … the link
between genes and personality. In spite of compelling evidence in its favour, there are
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objections to the theory that personality is genetically determined. I’ll just mention two for the moment. Both are based on weaknesses in twin studies as a research method. The first, as Borkenau comments, is that the majority of twin studies into genes and personality have been based on self- and peer-reporting. Of course, the main disadvantage of self-reporting is bias (a tendency to be influenced by personal preferences). Personally, I think Borkenau’s research is more convincing because his information is based on reports from detached observers, who assessed the behaviour of twins over a range of situations on video recordings. The second objection to twin studies as a research method is the question of how upbringing affects twins’ personalities. For example, twins brought up in the same environment may be similar for that very reason, rather than because they were genetically disposed to a certain personality.
On the other hand, there is more evidence of
the link between biology and personality. If we go back to Eysenck’s model … remember he created a two-dimensional model based on Jung’s theory of introversion and extroversion … we’ll find support for his work in experiments carried out in Sweden in 1980 … You can find this in Gleitman, again. More recent research, carried out by Schwartz in 2003, is described in Pervin. This study aimed to discover whether introverts or extroverts react differently to images of familiar and unfamiliar faces. The participants in the experiment were adults (but not twins, in this case) who had already been classified as introverts or extroverts when they were children. Their reactions to the images were measured on a fMRI (functional magnetic resonance imaging) scanner, an instrument for calculating brain activity. The results demonstrated quite clearly that the introverts were more sensitive to new stimuli than the extroverts.
I’m afraid we really have run out of time … which
is a pity, because I was planning to talk about the influence of environmental factors on personality as well. Anyway, I’ll sum up what we have covered in today’s lecture … we’ve looked at four theories of personality … trait theory, social-cognition, humanism and genetic inheritance … and we’ve had a look at ways of measuring personality.
Are there any questions so far? … No, good.
Now, when I see you in tutorials, we’ll look in more detail at personality theories. In the meantime, I’m going to set you a research task. Right, now listen carefully ... your task is to find out about the effect of environment on the development of personality. I’d like you to work
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