Classification for organisms is constantly changing because our technology is getting better. Classification used to be based on how similarly organisms appeared (morphological data). However, with better technology, we are able to look at the DNA of different species and are finding that the organisms we once thought to be closely related are not. Additionally, organisms we once thought to be distantly related may have very similar DNA.
Our classification now is based off of evolutionary history or phylogeny. Since evolution is so closely linked with genetics, our classification usually changes with new discoveries in DNA.
