Until very recently, human beings have been able to exercise little control over disease pathogens. They have helped pathogens find new hosts by creating networks of transportation, communication, and exchange, but they have provided these services unwittingly. They have had more conscious influence over the spread of plant and animal species, although these species too have often escaped human supervision and established independent footholds for themselves. Like the diffusion of disease pathogens, the spread of plants and animals has had a profound impact on human societies, and world historians have been able to chart the movements and effects of some species with tolerable precision.nineteenth centuries, a massive transfer of biological species took place following the European voyages of exploration that inaugurated sustained interaction between the peoples of the eastern hemisphere, the western hemisphere, and Oceania. As a part of this larger “Columbian exchange,” epidemic smallpox, measles, diphtheria, and other diseases exacted a devastating toll from indigenous peoples in the Americas and Oceania. Indeed, these massive transoceanic epidemics may have caused more deaths than any other agent in human history.