THE EFFECTS OF MINOR VARIATIONS IN THE ENVIRONMENT ON GENETIC EXPERIMENTS. To envision the kind of experiments that Nature would have to run to shed light on the economy, compare this article by Robert Sapolsky in the Wall Street Journal (August 11). Sapolsky describes the efforts of scientists to find out whether a particular gene affects anxiety in mice. To do so, “they generate a line of mice lacking Gene Z (“knockout” mice), plus another line with an extra copy of Gene Z (“transgenic overexpression” mice). Then they see if there’s something different about the behavior of either group when compared with unmanipulated control mice.”

The problem is that different labs get different results—some get a big effect, some no effect, some a negative effect.

Sapolsky gives the explanation that has been developed for these results: “Genes like our fictional Gene Z, with ‘neurogenetic’ effects on behavior, are often sensitive to small differences in the environment. Gene Z’s effects on anxiety might differ between two labs because the mice in the two are fed different kinds of food; nutrition influences brain chemistry and thus potentially Gene Z’s effects on the brain. Or maybe one of the labs uses a caustic disinfectant, or its doors bang loudly, and the mice there secrete more stress hormones, which alter the brain. Likewise with different temperatures, producing different levels of thyroid hormone.”

You can imagine how difficult it is to hold all the variables constant in performing an experiment.

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