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Y-DNA Haplogroup Atlas

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Haplogroup I

I-M170

Macro-haplogroup
I
Parent clade
F
Formed (estimate)
c. 35,000–45,000 years before present
TMRCA (estimate)
c. 25,000–30,000 years before present

Overview

Haplogroup I (I-M170) is the primary indigenous West Eurasian Y chromosome lineage of Europe. It represents a deep branch of the F derived radiation that likely formed somewhere in western Asia or southeastern Europe during the Upper Paleolithic, shortly after the initial spread of modern humans into the region. Unlike many other major West Eurasian clades that have clear Near Eastern or steppe associated expansion histories, I is distinctive in that the majority of its later diversification and demographic impact took place within Europe itself. By the Late Glacial and Mesolithic, I lineages had become tightly associated with European hunter gatherer populations. Ancient DNA surveys show that pre Neolithic western, central and southeastern Europeans were dominated by I derived lineages, with I2 in particular forming the backbone of Mesolithic paternal ancestry. Later, I1 became a key lineage of northern Europe, undergoing a pronounced expansion in the late Bronze Age and Iron Age and playing a central role in the genetic profile of Germanic and Scandinavian populations. As a result, haplogroup I is essential for understanding both the deep pre agricultural history of Europe and the later formation of historic European populations.

Geographic distribution

Today, haplogroup I is most frequent and diverse in Europe. Its two principal branches, I1 and I2, have complementary distributions. I1 reaches its highest levels in Scandinavia, Finland, Denmark and coastal regions around the North and Baltic Seas, with appreciable frequencies in Germany, the Netherlands, the British Isles and parts of central and eastern Europe. I2 is concentrated in southeastern and central Europe, the Balkans, the Carpathian Basin and parts of eastern Europe and Sardinia. Both branches are found at lower levels throughout much of the continent, reflecting complex demographic processes during the Neolithic, Bronze Age and Iron Age. Outside Europe, I occurs at low frequencies in the Near East, the Caucasus and the western steppe belt, usually as a result of back migrations from Europe or historical contacts. Small pockets of I are also present in diaspora populations in the Americas and Oceania, where they reflect recent European ancestry rather than ancient indigenous lineages.

Ancient DNA

  • Mesolithic hunter gatherer genomes from western, central and southeastern Europe frequently belong to I derived lineages, especially I2, making haplogroup I the dominant paternal ancestry in pre Neolithic Europe.
  • Early Neolithic farmers in Europe generally carry Near Eastern derived haplogroups such as G2a and J, but a subset of individuals show continuity of I lineages, indicating admixture between incoming farmers and local foragers.
  • Bronze Age and Iron Age samples from Scandinavia and northern Europe show rising frequencies of I1 associated lineages, reflecting the emergence and expansion of distinct northern European paternal profiles.
  • Later historic and medieval European genomes continue to show substantial representation of both I1 and I2, confirming long term persistence of haplogroup I despite steppe related and later demographic events.

Phylogeny & subclades

Within the F based Y chromosome tree, haplogroup I forms a deep branch parallel to J and G. Its internal structure is dominated by two major subclades: I1 (M253) and I2 (P215 and related markers). I1 is largely a northern European lineage with a relatively recent time to the most recent common ancestor compared to the overall age of I, suggesting a late Holocene expansion from a smaller ancestral population. I2, in contrast, preserves much of the older diversity within haplogroup I and contains numerous branches directly associated with European Mesolithic hunter gatherers. Basal I lineages that do not fall into I1 or I2 are extremely rare and are usually classified as I* in research trees. For atlas purposes, explicitly modeling I, I*, I1 and I2 as separate nodes makes it possible to connect deep time European hunter gatherer ancestry with later regionally specific paternal structures.

  • I* basal
  • I1 (M253)
  • I2 (P215 and related branches)

Notes & context

Haplogroup I is central to the reconstruction of European paternal history. It links Late Pleistocene and early Holocene hunter gatherers to later historic populations and provides a native European counterpart to the Near Eastern and steppe derived haplogroups that arrived with farming and later migrations.