This paper reviews the evolutionary and natural history of malarias; it is proposed that all human malarial parasites originated from zoonotic simian plasmodiids in tropical forests of southeastern Asia, during the terminal Pleistocene or early Holocene. The modes of malarial transmission among prehistoric natives of that geographic area is reconstructed, based primarily on ecological, archeological and ethnographic evidence. Early Holocene hunters and food gatherers of southeastern Asia shared the same forest habitats as several mosquito members of the Anopheles leucosphyrus group, known to be efficient malarial vectors. These forest dwellers could have maintained endemic malaria, however at low levels due to their low population density. With the abundance and interactive roles in transmitting human malaria of the An. dirus and An. minimus mosquitos in forest fringe areas, the middle Holocene settled farmers occupying such habitats would have been subject all year round to highly endemic malaria. Generally much lower and less uniform transmission of the disease could have been found among early coastal occupants, in the presence of the less efficient An. sundaicus vector. Malaria was practically absent on lowland floodplains, extensively occupied by human populations since the first millennium BC onwards, due to lack of major vectors.