In the pure Darwinian scenario of draconian selection that can exist for instance among microorganisms, which are numerous enough for drift and randomness not to be a factor, and among whom competence is maximized like in the ideal free market of liberal economists, all accidental extra copies of genes (paralogs) are eventually erased because they are inefficient.
But among a much smaller population, like humans, Darwinian evolution works inefficiently and these troublesome extra copies of genes do in fact persist. In principle paralogs are problematic and can cause degenerative diseases like Alzheimer because they produce less efficient proteins. But what Ariel Fernández and Jianping Chen of the University of Texas have found is that these paralogs also drive complexity, that it is the accumulation of these errors by drift what in fact generates complexity, that complexity can only arise when selective evolution becomes weak and drift (chaos) rules instead.
After all every order is just a subset of pure Chaos, right?
Source: Science Daily.
Original paper: Human capacitance to dosage imbalance: Coping with inefficient selection. Genome Research 2009 (paywall).