It seems likely, on the basis of this evidence, that haplogroup H entered Europe not much more than ∼20,000?25,000 years ago, and dispersed rapidly to the southwest of the continent. Although this was at the peak of the last Ice Age, a passage into Europe at this time is not implausible from an archaeological perspective, since there is evidence for extensive contacts between people of the Badegoulian culture of east-central Europe and those of southwest Europe.
Indeed, it now seems likely that the west European Magdalenian culture had its roots in the Badegoulian, and not in the local Solutrean of the western glacial refugium. It is the Magdalenian culture that is seen to expand dramatically from the Iberian refugium from ∼15,000 years ago in the radiocarbon record for western Europe, although Europe was probably never completely depopulated during the LGM (
Housley et al. 1997;
Terberger and Street 2002;
Gamble et al. 2004).
Haplogroup V was identified, on the basis of control-region sequences, as a likely marker of a human dispersal in Late Pleistocene Europe (
Torroni et al. 1998). Higher phylogenetic resolution of the lineages concerned clarified the geographic pattern by distinguishing the more derived haplogroup V from its ancestor, pre-V, which could now be seen to display a quite distinct phylogeographic pattern (
Torroni et al. 2001). Haplogroup pre-V appeared to have entered Europe from the east sometime around 20,000?25,000 years ago, at the time of the LGM. However, the diversity and frequency of the derived haplogroup V suggested that it had evolved from pre-V in western Europe, with its age suggesting an expansion from a glacial refuge in Iberia ∼15,000 years ago, accompanying the Magdalenian expansion.
It is clear that the phylogeographic patterns displayed by sub-haplogroups H1 and H3 both closely resemble that of haplogroup V. The star-like phylogenies, geographic distribution, and estimated ages of all three clades suggest that they all took part in a major expansion from southwest to northeast Europe ∼12,000?14,000 years ago. Between them H1 and H3 amount to around half of the haplogroup H samples in our coding-region database. They comprise ∼65% of haplogroup H lineages in Iberia, ∼46% in the northwest, ∼27% in central and eastern Europeans, and ∼5%?15% in the Near East/Caucasus, falling to zero in the Gulf. It is notable that the diversity does not fall within H1 moving from west to east, unlike the situation with haplogroup V (
Torroni et al. 2001), but a rapid expansion within the time-frame of the Magdalenian would in fact not be expected to result in a west-east diversity gradient. The cline seen in haplogroup V diversities most likely has its explanation in more recent founder events in the east.
The remaining haplogroup H lineages present a more complex pattern. The explanation must include the evolution of haplogroup H from its ancestor haplogroup HV, probably in the vicinity of the Near East (
Richards et al. 2000;
Loogv?li et al. 2004), and subsequent founder events in Europe, seen in H*. Minor sub-clades found in both Europe and the Near East (H4, H7, and H13) may also have entered Europe around the LGM, and/or during later dispersals from the Near East, such as the Neo-lithic. H must have given rise to H1 and H3 in the western refuge (analogous to ancestral lineages within haplogroup pre-V giving rise to haplogroup V;
Torroni et al. 2001), and itself appears very likely to have been partly redistributed alongside them by the late-glacial re-expansion, since an Atlantic European cluster clearly forms part of the H* phylogeny.
Several other minor sub-clades (H2, H5a, H6) also seem likely to have taken part in this process, and may also have evolved in western Europe: More data will be needed to trace their phylogeographic patterns more closely. Interestingly, however, the frequency profile of H5a suggests that, if indeed it has largely been distributed by late-glacial dispersals, this sub-haplogroup may trace a distinct dispersal route into central and eastern Europe. In contrast, H1 and H3 appear at least in part to have spread northwards fairly close to the Atlantic coastline, into the British Isles.
The mtDNA evidence therefore correlates well with Y-chromosome evidence for late-glacial expansions from a south-west European refugium (
Semino et al. 2000;
Rootsi et al. 2004). It indicates that the major demographic signal in the modern European mtDNA pool is the result of the expansion of hunter-gatherer populations at the end of the Palaeolithic, although this has not entirely erased the traces of earlier processes.