Figure 2.2 A phylogenetic tree of the Mus species group. All of the extant species within the Mus subgenus of the Mus genus are shown. Table 2.1 lists the other subgenera in the Mus genus. Domesticus, musculus, castaneus, and bactrianus are all subspecies within the M. musculus group. All other lines represent well-defined species. The geographical distributions of M. musculus subspecies are illustrated in Figure 2.3. The general distributions of all other species are indicated next to their names here. The indicated times of divergence between evolutionary lines in millions of years before present (myr BP) are consensus estimates based on data from various sources (Ferris et al., 1983b; Bonhomme, 1986; Berry and Corti, 1990; Boursot et al., 1993; Hammer and Silver, 1993).