Some animals have already sequenced their genomes. If at first it was enough to decode a single specimen of a species, now scientists are discovering that to know how the genome of a species has actually worked and evolved, several genomes must be compared. Therefore, the genomes of twelve specimens of the fly species Drosophila melanogaster have been decoded. When comparing the genomes obtained, it has been shown that sequences are essential for this species (those that appear in all specimens). Thus, they realize that hundreds of sequences to be included in the most important group had no importance when they had a single copy.