In Crosby's paper Germs, Seeds, and Animals, he makes the argument that the reason Europe was so able to take over the aboriginal civilizations of the world was more based on biological phenomenon of unidirectional migration rather than the Europeans being technologically or mentally superior. He makes his argument through the points of how human beings, animals, germs, and weeds spread over the new found territories. Crosby talks about how the flow of people was almost uniformly unidirectional. It was the peoples of Europe leaving Europe to these new and distant lands. This unidirectional migration across the seas to the colonies not only appears in the appearance of humans but with animals, germs and weeds.
Many animals that are now feral or highly connected with aboriginal peoples are not native to the lands of the new world. The Sioux tribes of the American plains never rode upon a horse until it was brought over by the Europeans. Hordes of feral pigs in the southern swamplands were unheard of until contact between natives and the Spanish occurred. Sheep ran unchallenged in New Zealand quickly out numbering even the human population that by 1836 "there where a million sheep"(33) living there. Though the people of Europe during this time had no knowledge of germ theory, the germs they brought with them from their homelands quickly spread and wiped out many thousands. It was so devastating that the only aboriginal populations that survived the epidemics was because their numbers were so strong to begin with (38). The only place where this didn't happen was New Zealand where by the time Europeans arrived in any significant numbers a vaccine for most of the most deadly pathogens had been found and brought along. Unbeknownst to the Europeans this was the most potent of all the reasons the colonization effort was so successful. The sole fact that diseases wiped out whole populations leaving no one to oppose the advancement of white settlements, Where by allowing the total takeover of the colonized lands.