We may not need to wait nearly so long.<p>This is a quote from a book by Nick Lane that I think would be relevant here.<p>&quot;studies show that bacteria can lose superfluous genes in a matter of hours or days. Such fast gene loss means that bacterial species tend to retain the smallest number of genes compatible with viability at any one moment.&quot;<p>The main reason he claims is that for bacteria, the speed of DNA replication is generally the limiting factor in speed of cell division and proliferation of said bacteria, so selection pressures lead to more favorable outcomes for the bacteria that maintain the smallest functional genome.<p>The book is <i>Power, Sex, Suicide: Mitochondria and the Meaning of Life</i> if you or anyone else is interested. Fascinating read I would recommend it.