This can speed up a search, and ensures that the hit list will only contain entries from the selected species. If the search data are marginal, and you are completely confident of the origin of the protein, this can help bring a weak match to the top of the list. Unfortunately, several of the major sequence databases do not use a rigorous system for specifying taxonomy. This can make it difficult to extract reliable species information. There may be multiple names for a single species - e.g. homo sapiens, human, man.
Names are sometimes misspelled - e.g. homo sapeins.
Continual re-classification of species is taking place. A non-redundant database may provide only one species identifier even though the entry represents identical sequences from several species. The top level classification, All entries , is self-explanatory. The three classsifications below Rodentia are Mus , Rattus , and Other rodentia . Selecting Other rodentia would limit a search to Rodentia excluding Mus and Rattus .