The temperate zones of North America and Oceania, as Crosby pointed out, were ideally suited to Eurasian crops and livestock; not only because of their climate, but because they possessed few native competitors and no local parasites, such as the various funguses, insects or field mice that have developed to specialize in sharing human-grown wheat. Unleashed on such fresh environments, Old World domesticates went into reproductive overdrive, even going feral again in some cases.
