Mystery of ancient DNA marker rewrites story of how humans first reached the Americas

One of the world's greatest genetic mysteries is how a DNA marker present in Europe reached North America, leaving no clear trail through Siberia or Alaska.

Scientists have been baffled by how Haplogroup X arrived more than 12,000 years ago, raising new questions about how the Americas were first populated.

Haplogroup X is a rare maternal DNA lineage, passed down from mother to child, found in both Europe and North America. 

Its unusual presence suggests that early Americans may have arrived in multiple waves, challenging the traditional view that all Native American maternal lineages came solely from Siberia via the Bering Land Bridge.

Today, the X2a branch of Haplogroup X is found in several Indigenous groups across North America, including the Ojibwe, Sioux, Nuu-chah-nulth, Navajo, and Yakama.

 It is also found in Europe and Western Asia, hinting at a far more complex migration history than previously thought.

Dr Krista Kostroman, a genetic medicine specialist and Chief Science Officer at The DNA Company, told the Daily Mail: “Haplogroups are like family seals. 

'They are distinctive genetic marks passed down over thousands of years, connecting us to ancestors who lived in entirely different landscapes, climates, and cultures. Because they rarely change, they serve as identifiers for tracing ancient migrations.'

Haplogroups A, B, C, and D are the most common maternal lineages among Native American populations. 

They each have distinct genetic signatures that trace back to different regions of East Asia and reflect separate waves of migration into the Americas during the late Ice Age. 

For example, haplogroup A is widespread among populations in North, Central, and South America, while B is more frequent in the Pacific Northwest and parts of Central and South America. 

Haplogroup C is concentrated in northern and western Indigenous groups, and D is found across North and South America but is particularly common in the Arctic and sub-Arctic regions. 

Together, these haplogroups provide a clear picture of the Asian origins of most Native American maternal lineages, which makes Haplogroup X’s unusual distribution all the more striking.

X2a appears among Indigenous groups in the Northeast and Great Lakes regions, while X1 is found primarily in North Africa, the Near East, and parts of the Mediterranean, though it remains rare even there.

'That rarity makes it a powerful clue for tracing human history,' Kostroman said. 'When an uncommon marker appears in distant, disconnected regions, it signals a shared connection in the deep past.'

Despite speculation, Haplogroup X does not prove Native American ancestry nor a direct European migration. 

Haplogroup X is rare in Siberia and Alaska, with some researchers suggesting that it represents an earlier migration, possibly via a coastal route. 

The most widely accepted theory is that X2a arrived in North America during the late Ice Age as part of migrations across the Bering Land Bridge from Northeast Asia, arriving alongside other maternal lineages. 

'Other possibilities are more speculative,' Kostroman noted. 'Small groups carrying Haplogroup X may have arrived earlier, or it may have entered the Americas in multiple waves alongside other lineages.' 

When Haplogroup X was first identified in the 1990s, its presence in Europe and among some Indigenous North Americans sparked controversy. 

Some researchers proposed a direct Atlantic crossing, known as the Solutrean hypothesis, though this has largely been dismissed. The X2a lineage differs from European and Near Eastern branches, reflecting a more complex migration history.

Parallels with other rare haplogroups further illustrate the complexity of human migration. 

Haplogroup C1b, found in North and South America but rare in Asia, provides clues about secondary migration waves. 

Haplogroup B2a, present in some Amazonian populations, shows deep diversification within the Americas. 

And Haplogroup U5, a rare European maternal lineage dating to the Ice Age, demonstrates how rare lineages can survive in isolated populations, much like X2a did in North America. 

Some groups have speculated that Haplogroup X supports religious or pseudoscientific claims, including theories linking Native Americans to Hebrew ancestry or the Book of Mormon. 

Others suggest Europeans may have crossed the Atlantic during the last Ice Age. Kostroman cautions against overinterpretation: 'Over the past two decades, Haplogroup X has shifted from being the centerpiece of bold trans-Atlantic theories to a subtle but powerful clue in understanding human prehistory. 

'It tells us that human migration was complex, involving multiple waves, exploratory groups, and connections across Eurasia long before people reached the New World.'