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Underground > Laboratory >

Nature and nurture and separating the two

lord henry strikes back

15:01 / 06.01.06

This is, in part, prompted by a report that I heard on radio 4 a few nights ago. Without going into too much detail (as it's not really important to my question) the report concerned a study regarding the relative affects of genetics and environment on personality. The test focused sets of twins, some identical and some not, some adopted together and others apart.

While (i feel unsuprisingly) identical twins who were adopted together showed the greatest similarities in personality, the next most similar group were identical twins adopted separately and not non-identical twins adopted together. The researchers used this to suggest that genes play a much bigger part than previously thought (I believe the figure they stated was that around 50% of personality traits could be traced to genetics).

Now this set me thinking: A lot of one's experiences (nurture) will be made up of interactions with other people. Like it or not we all react differently to people depending, in part, upon how they look - taller or stronger people are intimidating for example. On top of this the way an individual's appearance shapes up to certain social norms, beauty ideals etc, will also alter one's life experiences. As identical twins will, for the most part, look alike, how can the direct effects of genes on personality be separated from the resultant affects of ones genetically defined appearance?

Sorry, I know the above is a bit long and woffely. If anything is unclear just post and I will attempt to explain. I really would like to hear some opinions/answers from people working in the field.

Perfect Stranger

15:26 / 06.01.06

So what you are saying is that there are the social conditioning effects which come as a direct result of your genotype. Then there are the internal dispositions which are a result of your genotype.

You should also consider that there is a degree of overlap. For example you might be geneticly enclined to be higly competative; if you are also blessed with the genes to make sucsessful at this you might become a happy confident person. However if you have the same genes which determine this disposition but are lacking the genes which give you the physical prowes to follow it through; you might end up a unhappy, bitter person.

So in effect I suppose you could split the equasion into 3 parts, G; your genetic disposition. P; your phisical ability and C; your cultural enviroment.

Even in the case of identical twins you might find that a childhood illness causes factor P to be lacking and thus create very different personalities.

In biology there is Genotype - the genes you have and Phenotype - how you turned out. Some snails have idential genotypes but 3 different phenotypes of shell markings for example.

Now that's long and woffely man!

11:17 / 10.01.06

Science has never been my strong suit; I have even read a couple of books about genetics but most of it sailed over my head, and what didn't failed to stick. So, I can't add anything on the science front, but I can speak a little about identical twins and personality.

I have identical 2 year old twin boys. As I understand it this means that they are absolutely identical when it comes to their genes and DNA. Their nurture has been, if not identical, then extremely similar.

But over the course of the 2 years we have noticed differences in their personalities - one, for example, is a little more self-contained than the other and will happily be absorbed in playing on his own, while his brother will seek out company. One is readier with smiles for strangers while his brother is a little more shy. One is a reckless climber while the other keeps his feet on the ground. One will happily try new food, while his brother is a conservative eater. Obviously, this is fairly broad brush, and I can't be certain that I am not describing differences in behaviour rather than personality, but the totality is that I have 2 quite different little boys.

These personality/behavioural differences became apparent in the first year of their lives and I just can't for the life of me work out what accounts for the differences. Friends of ours also have identical twins around the same age and have noticed personality differences in their own children. For them, as practising Christians, they are proof of the existence of the soul, and, to be honest, I don't have a better answer.

09:48 / 12.01.06

As identical twins will, for the most part, look alike, how can the direct effects of genes on personality be separated from the resultant affects of ones genetically defined appearance?

lord henry, i'm not sure there is a meaningful distinction between "direct effects" and "resultant effects". I'm not in any way an expert in this area, but it seems to me that your genetic inheritance includes reactions to your appearance as well as reactions to the genetically-determined components of your intelligence, sexuality and whatever else. Or am I missing your point?

lord henry strikes back

09:20 / 13.01.06

Peoples reactions will be mediated by underlying social norms, such as the beauty ideal. A woman growing up in the UK who, in part thanks to her genes, is tall, slim, and blond will be seen as attracive, and men, for the most part, will behave favourably toward her. As a result of this she would probably be relatively confident (I know this is a simplified example but let's go with it for now). The same woman, or more precisely her twin, growing up in Sub-Saharan africa will be reacted to differently because of a different beauty ideal (which is not related to her genes) rather than her appearance (which is gene related).

However, most studies of twins are done in only one country for the simple reason that most sets of twins are adopted in the same country (the report that I refered to above was entirely based in the UK). As a result it will be hard to separate out the direct effects of genes from the interelationship of genes and social norms/generalised experience.

Hope that clears it up a bit.