It is the nature of science to change as new evidence is provided. Especially over the past 20 or so years, genetics has been providing more and more evidence on how closely some organisms are related, causing groupings to have to be adjusted (one or a few species having to be switched from one genus to another, etc.) The same thing occurred around the invention of the microscope. At the time, there were only 2 major groups of organisms--plants and animals. With the microscope came the investigation of microscopic structures, allowing scientists to find big enough differences between the fungi and plants to form another phylum. Eventually, bacteria and protists were also put into their own phyla. HOPE U GOT IT :)