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Friday, May 23, 2003

Overactive imagination

I've not had time to contribute to the current discussion about genetic engineering in humans due to the difficulties I've been having with experiments that involve genetic engineering in mice. But, in short, Bill McKibben and Ronald Bailey present opposing arguments (McKibben against, Bailey for). It seems to me that the entire discussion is moot because both seriously underestimate the complexity of the relationship between genes and behavior.

Thankfully this has been explained nicely by my colleague Charles Murtaugh, so all I have to do is nod my head in agreement. Particularly useful is his analogy about multigenic traits:

Consider the following analogy: you are standing in an orchard at night, a photographer's light meter in your hand. In front of you is a tree, giving off a certain amount of light as measured by the meter. That light represents the genetic component of the trait in which you're interested. It may come from a single bright lightbulb hung in the tree; without even looking up, you would be able to zero in on the bulb just by watching the light meter as you train it on different branches. The closer to the light, the higher the numbers on the meter. This is analogous to mapping a single gene trait, such as cystic fibrosis.

On the other hand, that same amount of light could be emitted by dozens of tiny Christmas tree bulbs; at a distance, the meter's reading is the same as with a single bulb, but as you move closer the numbers go haywire: now they are high, as the meter breezes very close to one bulb, but then it drops off with a single twitch of your wrist. Your frustration mounts: you know that there is light coming from the tree, but you can't pin down the sources.

Basically, the ability to fix, in a heritable sort of way, diseases that are caused by a single gene is on the very distant horizon. The ability to change traits that require multiple genes is not in the foreseeable future. And, most importantly, it is impossible to genetically alter traits that have nothing to do with genetics! Where anyone gets the idea that someone could engineer religious devotion into a child, I simply do not know.

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