Diseases, boy you're looking good, smallpox, I'm glad you've been eliminated. Animals, plants, and people. Mr. Green, Mr. Green, people are animals. Yeah, that's true, me, from the past, but just for the sake of simplicity we're- Also, if you think about it, microbes are kinda animals, and plants are too, I mean- Oh my god, shut up before I kill you and create a time travel paradox. Microbes, like those hairy blokes back there, were a definite negative in terms of the Columbian Exchange. Terminology is hard here, but the majority of Caribbean Islanders or Native Americans or Amerindians had exactly one response to the arrival of Europeans. Death.