Simpson's Paradox in a Synthetic Microbial System
John S. Chuang,*
Olivier Rivoire,
Stanislas Leibler
The maintenance of "public" or "common good" producers is a
major question in the evolution of cooperation. Because nonproducers
benefit from the shared resource without bearing its cost of
production, they may proliferate faster than producers. We established
a synthetic microbial system consisting of two
Escherichia coli strains of common-good producers and nonproducers. Depending
on the population structure, which was varied by forming groups
with different initial compositions, an apparently paradoxical
situation could be attained in which nonproducers grew faster
within each group, yet producers increased overall. We show
that a simple way to generate the variance required for this
effect is through stochastic fluctuations via population bottlenecks.
The synthetic approach described here thus provides a way to
study generic mechanisms of natural selection.
* To whom correspondence should be addressed. E-mail: chuangj{at}rockefeller.edu
