98,000–478,000) years ago. P. knowlesi underwent a rapid population growth between approximately 30,000 and 40,000 years ago. This era follows the growth in the human population in this area (~50,000 years ago). Branching order P. coatneyi and P. inui appear to be closely related to P. vivax. P. vivax and P. knowesli appear to have diverged 25–30 million years ago. P. gonderi appears to be basal in this clade. This is consistent with its African distribution rather than the mainly Asian distribution of the other species in this group. Several of the 'Asian' clade - Plasmodium coatneyi, Plasmodium cynomolgi, Plasmodium fragile, Plasmodium inui, Plasmodium fieldi, Plasmodium hylobati, Plasmodium inui, Plasmodium knowlesi and Plasmodium simiovale and an African species Plasmodium gonderi - have a single S-type-like gene and several A-type-like genes. It seems likely that these species form a clade within the subgenus Plasmodium. The 'Asian' species form a clade with P. simium and P. vivax being clearly closely related as are P. knowseli and P. coatneyi and P. fragile; similarly P. brazillium and P. malariae are related. P. hylobati and P. inui are closely related. P. fragile and P. gonderi appear to be more closely related to P. vivax than to P. malariae. An analysis of four apicoplast genome-encoded genes (small subunit rRNA, large subunit rRNA and caseinolytic protease C) of nine 'Asian' species (P. coatneyi, P. cynomolgi, P. fieldi, P. fragile, P. hylobati, P. inui, P. knowlesi, P. simiovale and P. vivax) and the African species P. gonderi suggests that P. coatneyi and P. knowlesi are closely related and that P. fragile is the species most closely related to these two. Also P. vivax and P. cynomolgi appear to be related. The pattern emerging from this data suggests that the ancestor of P. gonderi and the 'Asian' clade (P. coatneyi, P. cynomolgi, P. fieldi, P. fragile, P. hylobati, P. inui, P. knowlesi, P. simiovale and P. vivax) infected a primate host - perhaps the ancestor of the extant rhesus monkey - and migrated with its vertebrate host from Africa to Asia via the Middle East. The Asian branch then gave rise to several clades - P. fragile-P. coatneyi/P. knowlesi, P. hylobati/P. inui and P. cynomolgi - P. simium/P. vivax. P. fieldi, P. simiovale and P. vivax appear to be relatively early diverging species within this clade. P. fieldi and P. simiovale appear to be each other's closest relations. A