<P> Still, the effects of the introduction of European livestock on the environments and peoples of the New World were not always positive . In the Caribbean, the proliferation of European animals had large effects on native fauna and undergrowth and damaged conucos, plots managed by indigenous peoples for subsistence . </P> <P> European exploration of tropical areas was aided by the New World discovery of quinine, the first effective treatment for malaria . Europeans suffered from this disease, but some indigenous populations had developed at least partial resistance to it . In Africa, resistance to malaria has been associated with other genetic changes among sub-Saharan Africans and their descendants, which can cause sickle - cell disease . </P> <P> Before regular communication had been established between the two hemispheres, the varieties of domesticated animals and infectious diseases that jumped to humans, such as smallpox, were substantially more numerous in the Old World than in the New due to more extensive long - distance trade networks . Many had migrated west across Eurasia with animals or people, or were brought by traders from Asia, so diseases of two continents were suffered by all occupants . While Europeans and Asians were affected by the Eurasian diseases, their endemic status in those continents over centuries resulted in many people gaining acquired immunity . </P> <P> By contrast, "Old World" diseases had a devastating effect when introduced to Native American populations via European carriers, as the people in the Americas had no natural immunity to the new diseases . Measles caused many deaths . The smallpox epidemics are believed to have caused the largest death tolls among Native Americans, surpassing any wars and far exceeding the comparative loss of life in Europe due to the Black Death . It is estimated that upwards of 80--95 percent of the Native American population died in these epidemics within the first 100--150 years following 1492 . Many regions in the Americas lost 100% . The beginning of demographic collapse on the North American continent has typically been attributed to the spread of a well - documented smallpox epidemic from Hispaniola in December 1518 . At that point in time, approximately only 10,000 indigenous people were still alive in Hispaniola . </P>

In the short term which of these was the most influential element of the columbian exchange