Basic Local Alignment Search Tool is a type of search used by biologists to search for alignments of either protein sequences or nucleotide sequences with known seqences stored in the National Center For Biotechnology Information's databases. Such a search is invaluable to molecular geneticists because it will help to identify a sequence as a previously identified gene. To an evolutionary biologist, this is useful because showing that large sections of an organism's genome aligns with another organism's genome is strong evidence that both organisms shared a recent common ancestor.