From An Epidemic of Absence.

The scientific method that had proven so useful in defeating infectious disease was, by definition, reductionist in its approach. Germ theory was predicated on certain microbes causing certain diseases. Scientists invariably tried to isolate one product, reproduce one result consistently in experiments, and then, based on this research, create one drug. But we’d evolved surrounded by almost incomprehensible microbial diversity, not just one, or even ten species. And the immune system had an array of inputs for communication with microbes. What if we required multiple stimuli acting on these sensors simultaneously? How would any of the purified substances mentioned above mimic that experience? “The reductionist approach is going to fail in this arena,” says Anthony Horner, who’d used a melange of microbes in his experiment. “There are just too many things we’re exposed to.”

In an essay over ten years ago, I wrote,

E.D. Hirsch, Jr., writes, “If just one factor such as class size is being analyzed, then its relative contribution to student outcomes (which might be co-dependent on many other real-world factors) may not be revealed by even the most careful analysis…And if a whole host of factors are simultaneously evaluated as in ‘whole-school reform,’ it is not just difficult but, despite the claims made for regression analysis, impossible to determine relative causality with confidence.”

In the essay, my own example of a complex process that is not amenable to reductionist scientific method is economic development and growth. In that essay, I also provide a little game, like the children’s game “mastermind,” to illustrate the difficulty of applying reductionism in a complex, nonlinear world. Try playing it (it shows up better in Internet Explorer than in Google Chrome).

The phrase “causal density” is, of course, from James Manzi and his book, Uncontrolled.