Thursday, February 08, 2007

Nature v Nurture

There is a good diary over on Kos concerning the so-called nature vs. nurture debate. This is one of the more contentious, and in my opinion silliest, debate going on. There is a strong tendency to believe that given that each of these two things (nature and nurture, genes and environment) contribute to the characteristics an organism has each factor can be assigned some ranking, or percentage, of importance in the characteristics seen. This view is completely unfounded. I go into this in more detail here, but both genes and environment are 100% necessary and their role cannot meaningfully be divided into degrees of responsibility.

One comment to the diary, by aludlam, had this to say

But (and I'm being theoretical here, so don't slam me too hard)

If we could say with some level of confidence that one side of that equation is definitely less involved than the other, is it not prudent to come to the conclusion that the opposite factor is dominant?

eg - we look at 20 pairs of twins raised apart, and 19 of the pairs wind up having similar tastes in music, based on a survey of songs. We obviously don't have all the data on their development, but the end result leads us to believe that genetics plays a significant role in predisposition toward certain types of music - perhaps so much so that genetics determines the ear formations that determine what melodies are appealing absent some aversion event (eg, one of the 20th pair of twins got dropped on his head while listening to Mozart as a baby).

We can't measure these things except in the objective. Doesn't mean the objective is a worthless measurement. Just that more care is needed in interpreting the results.

To which I responded

Part of the problem is, what range of environments are you considering. See "environment" is not a single thing, but a near infinite range of possible things. If you could have a measure of the ability of identical twins to correctly identify faces at a given age and at 30 feet, say, taken throughout human history. You would find an exceedingly strong correlation with genetics, because that ability is largely determined by the shape of the eye, which is set by genes. But you would also have a large group of folks (since the invention of eyeglasses and in places where glasses are available) for whom the correlation would disappear. How does one classify that in terms of nature vs. nurture?

There is just no meaningful way for us to describe the degree to which "environment" can affect a characteristic when there are so many possible "environments".

I occurs to me that another analogy might help as well. Trying to assign a degree of responsibility to genes and environment is about as useful as trying to assign degree of responsibility to air, fuel and spark in the operation of your car's engine. Each is essential and the running of your engine is a result of the interaction between the three. Changing, or removing, any of the three will affect your engine's performance, but we cannot say that it's running is 33% due to the fuel, 33% due to the air and 33% due to the spark. Nor can we make amy more sense by assigning different percentages. It just is not a sensible way to understand how these components relate. A similar relationship holds for genes and environment.

But also note that I am in no way saying that because we can't assign some particular percent responsibility to genes that therefore they do not matter. This makes no more sense than to say that because we cannot assign a particular percentage responsibility to fuel in your car's engine, that therefore fuel does not matter. It again is just not the way these things work.

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