MALARIAS EVE - EVIDENCE OF A RECENT POPULATION BOTTLENECK THROUGHOUT THE WORLD POPULATIONS OF PLASMODIUM-FALCIPARUM

We have analyzed DNA sequences from world-wide geographic strains of P lasmodium falciparum and found a complete absence of synonymous DNA po lymorphism at 10 gene loci. We hypothesize that all extant world popul ations of the parasite have recently derived (within several thousand years) from a single ancestral strain. The upper limit of the 95% conf idence interval for the time when this most recent common ancestor liv ed is between 24,500 and 57,500 Sears ago (depending on different esti mates of the nucleotide substitution rate); the actual time is likely to be much more recent. The recent origin of the P. falciparum populat ions could have resulted from either a demographic sweep (P. falciparu m has only recently spread throughout the world from a small geographi cally confined population) or a selective sweep (one strain favored by natural selection has recently replaced all others). The selective sw eep hypothesis requires that populations of P. falciparum be effective ly clonal, despite the obligate sexual stage of the parasite life cycl e. A demographic sweep that started several thousand Sears ago is cons istent with worldwide climatic changes ensuing the last glaciation, in creased anthropophilia of the mosquito vectors, and the spread of agri culture. P. falciparum may have rapidly spread from its African tropic al origins to the tropical and subtropical regions of the world only w ithin the last 6,000 years. The recent origin of the world-wide P. fal ciparum populations may account for its virulence, as the most maligna nt of human malarial parasites.