The Iriomote cat's karyotype, the restriction fragment length of the ribosomal RNA (rRNA), and molecular phylogenetic analyses of the mitochondrial 12S rRNA and cytochrome b have proven to be identical, or nearly so, to the leopard cat's. The two cats are assumed to be extremely closely related, their differences being categorized as either intraspecies variations or individual mutations. Also, from the speed of cytochrome b's base-pair substitution and its diversity, it is estimated that the Iriomote cat diverged from the leopard cat around 180,000-200,000 years ago. According to marine geologists, the Ryukyu Islands were connected to mainland Asia via a land bridge from about 20,000 years ago to 240,000 years ago. Scientists believe that the Iriomote cat moved its range to the islands during this period. Because of this, it is assumed that there is little genetic variety within the species.