mtDNA sequence variation was studied in 419 individuals from nine Eurasian populations, by high-resolution RFLP analysis, and it was followed by sequencing of the control region of a subset of these mtDNAs and a detailed survey of previously published data from numerous other European populations. This analysis revealed that a major Paleolithic population expansion from the "Atlantic zone" (southwestern Europe) occurred 10,000-15,000 years ago, after the Last Glacial Maximum. As an mtDNA marker for this expansion we identified haplogroup V, an autochthonous European haplogroup, which most likely originated in the northern Iberian peninsula or southwestern France at about the time of the Younger Dryas. Its sister haplogroup, H, which is distributed throughout the entire range of Caucasoid populations and which originated in the Near East approximately 25,000-30,000 years ago, also took part in this expansion, thus rendering it by far the most frequent (40%-60%) haplogroup in western Europe. Subsequent migrations after the Younger Dryas eventually carried those "Atlantic" mtDNAs into central and northern Europe. This scenario, already implied by archaeological records, is given overwhelming support from both the distribution of the autochthonous European Y chromosome type 15, as detected by the probes 49a/f, and the synthetic maps of nuclear data.