“These changes are all fundamentally Darwinian. This point is worth repeating: taking any fast or instant evolutionary shifts as a refutation of the slow, gradual changes we associate with Darwin's vision is a fatal mistake because these quick shifts are still powered by gradualism. The woodrats might have been able to resist creosote by picking up the right bacteria, but those strains had to evolve the ability to break the insecticide on their own. Form their perspective, evolution proceeded through the usual stepwise way; from the host's perspective, everything happened in a flash. That is the power of symbiosis: it allows gradual mutations in microbes to produce instant mutations in hosts. We can let bacteria do the slow work for us, and then quickly change ourselves by associating with them. And if these alliances are beneficial enough, they can spread with blinding speed.”