Monday, July 9, 2007
Nature and Nurture
Not for nothing, but I thought it might be a good time to share a little lesson from quantitative genetics.
You here people talk about genes for thinks a lot, the “gene for blue eyes”, the “gay gene”, “the warrior gene” or even “the god gene”. In fact, most genes are not nearly as deterministic as all that. Interesting traits like personality, height and even intelligence result from the complex interplay of the genes you inherit from your parents and the environement those genes are expressed against. Sometimes this leads people into a false dichotomy, imagining that there is in some way a debate between how much nature and nurture contribute to some trait or other (the big three it seems are homosexuality, criminality and intelligence). The interplay between genes (which impart make the environment against which they are expressed) and environment is far too complex to allow the relative importance of either to split. In fact, the degree to which a given trait is genetically programmed is dependant on the environment against which the genes are expressed.
Lets take a crude example that equates to the way most people imagine genes and environment interact to give a trait (to be topical well use ‘intelligence’ which readers can define for themselves):
On the bottom axis we have some measure of how well an environment fosters intelligence (I guess good education systems, books at home and parents that value intelligence) and the vertical axis there is some metric of intelligence (lets say something like ‘g’ or IQ) The red line tells us how intelligent someone will be in each environment if they have the ‘genius’ gene and the blue line the same for the ‘dullard’ gene (did I mention this was a gross simplification). In this case putting a little extra effort into education (the environment score) helps the dullards out just a bit more than it does the geniuses. The end result is the same though; no matter how permissive the environment we would still say that intellect is controlled by these two genes.
Now, imagine that everyone experiences an environment that fits with about 18 in our made up intelligence-fostering axis.
This is very different! In this new environment the dullard and genius genes have no effect on the intelligence of their holders. Without changing anything except the environment the genes are expressed against a trait has moved from being completely genetically determined to having nothing to do with genes! How are we to rate the relative importance of nature and nurture if genes contribute to the environment and the environment determines how genetically determined a trait is. Seems to me like a good question to think about if you want to add to 8 generations of fear of a coming genetic meltdown or declare homosexuality to be ‘in the genes’ or ‘not’.
On the bottom axis we have some measure of how well an environment fosters intelligence (I guess good education systems, books at home and parents that value intelligence) and the vertical axis there is some metric of intelligence (lets say something like ‘g’ or IQ) The red line tells us how intelligent someone will be in each environment if they have the ‘genius’ gene and the blue line the same for the ‘dullard’ gene (did I mention this was a gross simplification). In this case putting a little extra effort into education (the environment score) helps the dullards out just a bit more than it does the geniuses. The end result is the same though; no matter how permissive the environment we would still say that intellect is controlled by these two genes.
Now, imagine that everyone experiences an environment that fits with about 18 in our made up intelligence-fostering axis.
This is very different! In this new environment the dullard and genius genes have no effect on the intelligence of their holders. Without changing anything except the environment the genes are expressed against a trait has moved from being completely genetically determined to having nothing to do with genes! How are we to rate the relative importance of nature and nurture if genes contribute to the environment and the environment determines how genetically determined a trait is. Seems to me like a good question to think about if you want to add to 8 generations of fear of a coming genetic meltdown or declare homosexuality to be ‘in the genes’ or ‘not’.
2 Comments:
I not so sure about this David.
Apart from anything else what exactly is intelligence?
I suspect the best measure is how successfully an individual integrates with his or her environment.
The ability to solve non linear differential equations may be a mark of intelligence in our society, especially if the individual with this skill is employed in engineering or economics etc.
However such an individual may well be socially dumb (its not unknown is it).
And such an individual will look incredibly dumb if forced to live amongst the natives of the Kalahari desert where the ability to solve such equations is near to useless in terms of survival and finding food and water is the important thing.
Apart from anything else what exactly is intelligence?
I suspect the best measure is how successfully an individual integrates with his or her environment.
The ability to solve non linear differential equations may be a mark of intelligence in our society, especially if the individual with this skill is employed in engineering or economics etc.
However such an individual may well be socially dumb (its not unknown is it).
And such an individual will look incredibly dumb if forced to live amongst the natives of the Kalahari desert where the ability to solve such equations is near to useless in terms of survival and finding food and water is the important thing.
Andrei,
I probably didn't ram home the point enough. All the numbers are made up, the braininess axis could be height or finger length, intellegence was the example I used because of Prof. Flynn's recent comments.
My point is that even if there really is a gene that was contributing a real trait that fits the meaning most western types put to intellegence it still wouldn't mean there was a 'hard-wired' genetic basis to that trait. That and the fact that environment even determines how genetically determine (heritiable) a trait is.
Given those facts Nature/Nuture becomes very hard to untangle
I probably didn't ram home the point enough. All the numbers are made up, the braininess axis could be height or finger length, intellegence was the example I used because of Prof. Flynn's recent comments.
My point is that even if there really is a gene that was contributing a real trait that fits the meaning most western types put to intellegence it still wouldn't mean there was a 'hard-wired' genetic basis to that trait. That and the fact that environment even determines how genetically determine (heritiable) a trait is.
Given those facts Nature/Nuture becomes very hard to untangle
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