Genome complexity is correlated with biological complexity. A recent paper by Michael Lynch proposes that evolution of complex genomic architecture was driven primarily by non-adaptive stochastic forces, rather than by adaptive evolution.1 A general negative relationship between selection efficiency and genome complexity provides a strong support for this hypothesis. The broad capacity of this theory is both its appeal and source for criticism. BioEssays 28: 979–982, 2006. © 2006 Wiley Periodicals, Inc.