Evolution of species, whether bacterial, plant or animal, diverged from the American and the Eurasian continent. Thus, the New Continent did not have the germs responsible for a large number of infectious diseases such as chickenpox, influenza and malaria among others. The transfer of animals and plants from both sides of the Atlantic, as well as the germs, has been called the most important event in modern history.

The spread of diseases brought by the Europeans explains the collapse of the Amerindian population and the import of African slaves to replace them as they were immunized from these diseases.