As humans began to re-populate Western Europe after the ice age, by far the most frequent mtdna lineage carried by these expanding groups was haplogroup H, which would come to dominate the European female landscape. Today, haplogroup H comprises 40-60% of the gene pool of most European populations. In Rome and Athens, for example, H is found in about 40% of females, and it exhibits similar frequencies throughout Western Europe. Moving eastward the frequencies of H gradually decrease, illustrating the migratory path these settlers followed as they left the Iberian peninsula after the ice sheets had receded. Haplogroup H is found at around 25% in Turkey and around 20% in the Caucasus mountains. While haplogroup H is considered the Western European lineage due to it's high frequency there, it can also be found much further east. Today, it comprises around 20% of southwest Asian lineages, about 15% of people living in Central Asia, and around 5% in northern Asia. Importantly, the age of haplogroup H lineages differs quite substantially between those seen in the west compared with those found in the east. In Europe it's age is estimated at 10,000-15,000 years old, and while H made it into Europe substantially earlier (30,000 years ago), reduced population sizes resulting from the last ice age significantly reduced it's diversity there, and thus it's estimated age. In central and east Asia however, it's age is estimated at 30,000 years old, meaning the lineage made it into those areas during some of the earlier migrations out of the near east. Today, the single highest frequency of haplogroup H in any country is to be found in Ireland, where 65% of females belong to H.
