Parasitism Definition Parasitism: is a phenomenon that occurs when organisms, such as plants or animals, take advantage of another organism without giving any benefit to it. This involves the parasite relying on its food resources and survival, often resulting in harm or destruction to the host organism. History and Evolution The history of parasitism spans centuries and research into it is ongoing. Parasitism has evolved over time, with some parasitic organisms forming complex relationships with their hosts. For example, studies have shown how parasites have adapted to the environment and lifestyle of their hosts, resulting in significant impacts on ecosystems.