The Genome Speaks: Origins of the Japanese

In 1991, the physical anthropologist Hanihara Kazuro proposed what would become the long-standing orthodoxy on the origins of the Japanese people: the Dual Structure Model.

The model posits that modern Japanese arose from the admixture of two distinct populations -- the Jomon, who first inhabited the Japanese archipelago, and the Yayoi, continental migrants who arrived via the Korean Peninsula beginning around 900 BCE.

The Jomon had cultivated a unique culture for some sixteen thousand years, producing among the world's oldest known pottery. Deep-set features, double eyelids, wet earwax -- these physical traits persist most visibly today among the Okinawan and Ainu peoples.

The Yayoi migrants, by contrast, introduced wet-rice agriculture and metalworking, fundamentally transforming the culture of the archipelago. Elongated faces, single eyelids, dry earwax -- characteristics found with particular frequency among modern inhabitants of the Kinki region.

In September 2021, an international research team led by Gakuhari Takashi of Kanazawa University published a landmark paper in Science Advances.

Through genomic analysis of ancient skeletal remains, they demonstrated that the origins of the Japanese people follow not a dual but a triple structure.

The first layer is Jomon -- people who separated from a basal continental population some twenty to fifteen thousand years ago and settled across the archipelago. The second layer is Northeast Asian -- migrants who arrived during the Yayoi period via the Korean Peninsula, bringing wet-rice agriculture. And the third layer -- East Asian. A population that arrived during the Kofun period (3rd to 7th century CE), one that had been entirely overlooked until now.

The decisive finding was this: the genome of Kofun-period skeletal remains closely matched that of modern Japanese. In other words, the genetic foundation of today's Japanese was not laid during the Yayoi period but during the Kofun period.

This discovery lent genetic confirmation to the historical significance of the Kofun era -- an age when colossal keyhole-shaped burial mounds appeared abruptly and the Yamato polity unified the archipelago.

In April 2024, RIKEN (Japan's premier research institute) published a study in Science Advances that validated the Triple Structure Model using large-scale modern data.

Whole-genome sequencing of 3,256 Japanese individuals revealed three distinct ancestral components, confirming the tripartite framework with unprecedented resolution.

K1 (Okinawan lineage): the component retaining the strongest Jomon genetic signature, highest in Okinawa Prefecture. K2 (Tohoku lineage): closest to Northeast Asian ancestry, peaking in Akita and Aomori. K3 (Kansai lineage): closest to East Asian ancestry, reaching its highest proportion in Shiga Prefecture.

What makes this striking is how sharply these three components vary by prefecture. Okinawa shows a pronounced K1 dominance; Shiga leads in K3. Unexpectedly, the entire Shikoku region also registers a high K3 (continental migrant) ratio.

When this prefecture-by-prefecture genetic map is overlaid with shrine distribution patterns, the correlations are nothing short of astonishing -- a subject explored in the next chapter.

In October 2024, a team led by Professor Ohashi Jun of the University of Tokyo published an important challenge to the Triple Structure Model.

Their whole-genome analysis of Yayoi-period migrant remains from the Doigahama site in Yamaguchi Prefecture revealed that Yayoi-era migrants already carried both Northeast Asian and East Asian genetic components.

The implications are profound. Where the Triple Structure Model envisions Northeast Asians arriving in the Yayoi period and East Asians arriving separately in the Kofun period, this finding suggests that an already mixed population may have migrated as a single wave during the Yayoi era.

In other words, the three ancestral "waves" may not have been distinct arrivals at all -- the migrants themselves may have been a genetically diverse, already-blended population from the start.

This debate remains unresolved. Further ancient DNA analysis from additional skeletal remains will be the key to reaching a definitive answer.

Professor Ohashi Jun's team at the University of Tokyo calculated a 'Jomon ancestry index' for each prefecture -- a quantification of how much Jomon genetic heritage persists among each region's inhabitants.

The highest Jomon ancestry belongs to Okinawa Prefecture, followed by the prefectures of the Tohoku region. At the opposite end, the highest continental-migrant ratio (lowest Jomon ancestry) is found in Shiga Prefecture, with the broader Kinki region showing strong continental influence throughout.

There are surprises. Shikoku as a whole shows unexpectedly high continental ancestry. And Hokkaido, despite the presence of the Ainu people, registers values close to the Honshu average -- likely a consequence of later Wajin (mainland Japanese) settlement.

When this genetic map is overlaid with shrine distribution data, a fascinating pattern emerges: Hachiman-lineage shrines tend to concentrate in regions with high continental-migrant ratios, while Suwa-lineage shrines cluster in areas of high Jomon ancestry. The correlation between genetics and faith will be explored in depth in the next chapter.

Extracting DNA from human remains thousands of years old is a task of formidable difficulty. Ancient DNA fragments over time, contaminated by microbial and soil DNA. What researchers work with is often a degraded sliver amounting to less than one percent of the full genome.

The breakthrough came with Next-Generation Sequencing (NGS). Where the earlier Sanger method struggled with fragmented ancient DNA, NGS processes vast quantities of short fragments in parallel, assembling them like pieces of a puzzle. From the 2010s onward, this technological revolution drove an explosion in ancient genome research.

Japan presents its own unique challenges. The hot, humid climate severely degrades DNA preservation. High-quality genome data was recovered from approximately 3,800-year-old Jomon remains at the Funadomari site on Rebun Island, Hokkaido -- but this was an exceptional success owed to the cold climate. South of Hokkaido, extracting DNA from remains of comparable age is often impossible.

In recent years, however, a technique for efficiently extracting DNA from the petrous bone of the temporal bone -- an extraordinarily dense bone surrounding the inner ear -- has been established, dramatically improving success rates. The era when ancient genome research in Japan was deemed impossible is, at last, drawing to a close.

What first astonished researchers upon analyzing the Jomon genome was its profound isolation. The Jomon are genetically distant from every modern population on Earth. They diverged from mainland East Asians more than twenty thousand years ago -- one of the deepest splits among all living human groups.

Yet they were not entirely alone. A degree of genetic affinity has been confirmed with the bearers of the Hoabinhian culture, ancient hunter-gatherers of Southeast Asia. The Hoabinhian was a lithic culture that flourished across the Indochinese Peninsula from roughly 44,000 to 4,000 years ago -- people who, like the Jomon, sustained a hunter-gatherer way of life across vast stretches of time.

This genetic connection suggests that the ancestors of the Jomon reached the archipelago not only via a northern route through Siberia but also along a southern route, island-hopping northward from Southeast Asia. During the last glacial period, sea levels were approximately 120 meters lower than today, and the islands of Southeast Asia were joined as a single landmass. From this vast continent known as Sundaland, people may have journeyed north.

The genetic singularity of the Jomon -- their deep divergence from continental East Asians, their affinity with ancient Southeast Asian peoples, and over ten thousand years of independent evolution on the archipelago -- proves genetically that the 'Japanese' are not simply a subset of East Asia.

It was precisely this singularity that, when blended with later Yayoi and Kofun-period migrants, gave rise to a genetic mosaic unlike anything else in the world.

Your immune system is a ledger of every pathogen your ancestors ever fought. And that ledger sometimes tells a story quite different from the one revealed by whole-genome analysis.

HLA (Human Leukocyte Antigen) genes govern how the immune system distinguishes self from non-self. They constitute the most polymorphic region of the human genome and determine organ transplant compatibility -- but they are simultaneously a precision mirror of a population's evolutionary history.

Research by Professor Tokunaga Katsushi of Tokai University and colleagues has identified several HLA haplotypes characteristic of the Japanese. Most notable is HLA-A24-B52-DR15, carried by approximately 12% of the Japanese population yet exceedingly rare among Chinese and Korean populations, and concentrated almost exclusively on the Japanese archipelago worldwide.

One hypothesis holds that this haplotype was selected during the Jomon people's long adaptation to pathogens endemic to the archipelago's hot, humid forests -- viruses and parasites that flourished in the dense woodland environment. More than ten thousand years of genetic isolation produced an immunological evolutionary path distinct from all other Asian populations.

What makes HLA particularly revealing is that it evolves under balancing selection rather than genetic drift. While most of the genome trends toward homogenization in isolated populations, HLA diversifies in response to each new pathogen threat. The Jomon's HLA did not merely record where they came from; it recorded what they fought. Where whole-genome analysis narrates the history of human migration, HLA narrates the history of war against disease -- two different chronicles bound within the same DNA.

Intriguingly, certain HLA haplotypes are associated with susceptibility to autoimmune diseases. The relatively high incidence of rheumatoid arthritis and Graves' disease among the Japanese is not unrelated to this immunogenetic singularity. The weapons ancestors won in ancient battles now act upon the modern body in unexpected ways.

There is one decisive gap in Japanese genomic research: the restriction on investigating imperial tombs.

The Imperial Household Agency administers 896 burial sites across the nation. Of these, 188 are classified as 'imperial mausolea' (tombs of emperors and empresses) and 555 as 'imperial graves' (tombs of other members of the imperial family). Academic investigation of the vast majority is effectively prohibited, placing them beyond the reach of ancient DNA research.

In 2008, sixteen academic organizations including the Japanese Archaeological Association petitioned the Imperial Household Agency for limited access and permission to conduct scholarly surveys. As a result, observational visits to the outer perimeters of select sites were permitted -- but excavation and DNA sampling remain forbidden to this day.

Why does this matter? As the Triple Structure Model revealed, Kofun-period migrants defined the modern Japanese genome. Yet the genetic roots of the very center of Kofun-period power -- the Yamato court, the imperial house -- have never been scientifically examined. The tomb attributed to Emperor Nintoku (Daisen Kofun), one of the largest burial mounds on Earth, has never undergone a comprehensive academic excavation.

It is precisely this 'zone of the unexaminable' that has become the breeding ground for urban legends claiming foreign origins for the imperial family -- theories linking the Japanese to ancient Israel, or tracing the imperial line to Sumer. The more science advances, the more the imagination swells around what remains beyond investigation. This is the structural mechanism of urban legends itself. The academic opening of imperial tombs could provide definitive evidence in the debate over the origins of the Japanese, but the day that door opens remains nowhere in sight.

Y-chromosome haplogroup D displays one of the most extraordinary distribution patterns among all human lineages. It is found at high frequency in only two populations: the Japanese (approximately 35-40%) and the Tibetans (approximately 40-50%). Two peoples separated by vast geography -- yet sharing the same ancient lineage at remarkably high rates.

The prevailing hypothesis runs as follows: the ancestral population carrying haplogroup D left Africa some 60,000 to 70,000 years ago and migrated eastward along the southern rim of Eurasia from South Asia. They once ranged across broad swaths of East Asia but were subsequently displaced by later-expanding groups (notably haplogroup O). The Japanese archipelago, shielded by ocean, and the Tibetan Plateau, shielded by mountains, both limited the influx of later populations -- functioning as refugia where the ancient lineage survived.

In genetic terms, the Japanese D lineage is classified as D1a2a (formerly D1b), while the Tibetan lineage is D1a1 (formerly D1a) -- branches of the same root that diverged tens of thousands of years ago. The precise formulation, then, is not that 'the Japanese and Tibetans are close relatives' but that 'both are descendants of an ancient lineage that branched from a common ancestor.'

Notably, Y-chromosomes extracted from Jomon skeletal remains show a high probability of belonging to the D lineage, while Yayoi-migrant remains yield predominantly O-lineage results. The concentration of D-lineage thus serves as another index of a region's 'Jomon ancestry.' The elevated D-lineage frequencies among Okinawan and Ainu populations are fully consistent with whole-genome analyses.

A caveat is in order, however. The Y-chromosome reflects only paternal inheritance and therefore reveals merely one dimension of a population's history. Only by combining it with maternal mitochondrial DNA and autosomal analysis does the full picture of Japanese origins come into view.

The genome does not merely narrate the past of your ancestors -- it acts directly upon the body you inhabit today. The genetic composition of the Japanese produces distinctive patterns of susceptibility to specific diseases.

Consider alcohol metabolism. The ALDH2*2 variant -- an inactive form of the aldehyde dehydrogenase enzyme common in East Asian populations -- is carried by approximately 40% of Japanese. This variant, believed to have been introduced by Yayoi-period migrants, is responsible for the 'Asian flush' reaction to alcohol. Among populations with high Jomon ancestry, such as the Okinawans and Ainu, the frequency of this variant is notably lower. Your tolerance for alcohol, it turns out, is a mirror of the Jomon-to-migrant ratio within you.

The BioBank Japan project, led by RIKEN, has accumulated genetic and clinical data from approximately 270,000 Japanese individuals. Analysis has identified numerous disease-susceptibility variants specific to the Japanese population. Risk variants for type 2 diabetes, rheumatoid arthritis, and atrial fibrillation, among others, operate against a genetic background fundamentally different from that of European populations.

Equally significant are differences in drug response. Reactions to certain anticancer agents and immunosuppressants vary markedly depending on genetic background. Medications developed in the West do not necessarily produce the same effects in Japanese patients, and conversely, developing drugs particularly effective for the Japanese requires a deep understanding of the Japanese genome.

The ancestral diversity illuminated by the Triple Structure Model has direct consequences for modern medicine. The three genetic components -- Jomon, Yayoi, and Kofun-period migrant -- shape your disease risks, your drug responses, and your physical traits. The genome is not merely a chronicle of the past; it is a text that inscribes your present and your future.

At every drinking gathering, there are those whose faces turn crimson after a single sip. If you are one of them, your body is the living embodiment of an evolutionary enigma.

Alcohol is first metabolized in the body into acetaldehyde, then converted by the enzyme ALDH2 (aldehyde dehydrogenase type 2) into harmless acetic acid. Individuals carrying a single-nucleotide variant known as rs671 (ALDH2*2) have dramatically reduced enzyme activity. Acetaldehyde accumulates, triggering facial flushing, palpitations, and nausea -- the so-called 'Asian flush.'

The geographic skew of this variant is striking. Approximately 40% of Japanese carry it, as do 30-40% of Han Chinese in southern China and 25-30% of Koreans. Among Europeans, Africans, and South Asians, it is virtually absent. It is a 'non-drinker gene' concentrated exclusively in East Asia.

Why would a seemingly disadvantageous mutation spread to such high frequencies? The most compelling hypothesis is co-evolution with rice cultivation. Wet-rice agriculture, which began in the Yangtze River basin roughly ten thousand years ago, created paddy environments ideal for mosquito breeding, spreading malaria and other infections. The ALDH2*2 variant naturally limits alcohol consumption by making drinking unpleasant, reducing deaths from alcohol dependence and intoxication-related accidents. Some studies further suggest that elevated acetaldehyde levels may inhibit the replication of the malaria parasite.

Within the Japanese archipelago, the distribution of this variant maps neatly onto the Triple Structure Model. Populations with high Jomon ancestry -- Okinawans and Ainu -- show low ALDH2*2 frequency. The Kinki region, with its high continental-migrant ratio, shows high frequency. Your tolerance for alcohol is, in effect, the most accessible genetic indicator of the Jomon-to-migrant ratio within you.

A powerful counterargument notes that molecular-clock estimates for the emergence of ALDH2*2 range widely, from 2,000-3,000 to 7,000-10,000 years ago. If the variant predates rice cultivation, the co-evolution narrative weakens. Moreover, India and Southeast Asia -- where rice farming flourishes -- show virtually no presence of this variant. Yet the hypothesis survives because the variant's emergence and its selective expansion are separate events: even if the mutation arose before agriculture, its rapid spread may have been driven by survival advantages within rice-farming societies.

The next time your face flushes red at a gathering, remember: that redness may be the remnant of a 'survival device' your ancestors acquired ten thousand years ago, when they began cultivating rice in a perilous environment.

Of your entire DNA, the regions that encode proteins constitute a mere two percent. The remaining ninety-eight percent was long dismissed as 'junk DNA' -- evolutionary debris, serving no purpose. So it was believed.

In 2012, the international ENCODE project overturned this assumption at its foundations. Over four years, 442 researchers scrutinized all three billion base pairs, and what they found was that roughly eighty percent of the so-called 'junk' regions carry biochemical function. They are regulatory switches -- determinants of when, where, and which genes are activated.

The implication is that DNA resembles not so much a blueprint as a musical score. The same score, played with different dynamics and emphases, yields entirely different music. The non-coding regions provide those performance instructions. Epigenetics -- the mechanism by which gene expression is altered without changing the DNA sequence itself -- can be rewritten by environment, diet, stress, and even the experiences of one's ancestors.

In 2013, a research team at Emory University published a startling animal study. Mice were conditioned to associate a particular odor with electric shock. Their offspring -- a generation that had never experienced the stimulus directly -- exhibited fear responses to the same odor. The memory of fear had been 'inherited' through epigenetic modification.

If this mechanism applies to humans as well, then consider: the Jomon people's fifteen-thousand-year accumulation of attunement to the natural world, the continental memories carried by Yayoi migrants, the statecraft wisdom brought by Kofun-period arrivals -- these may not be merely cultural inheritance. They may be inscribed as epigenetic traces in the non-coding regions of your DNA. The 'silence' of that ninety-eight percent may be an archive in which tens of thousands of years of ancestral experience lies sleeping.

Sixteen thousand five hundred years ago, as the last ice age loosened its grip on the Japanese archipelago, something happened that had never occurred anywhere on Earth. Someone shaped wet clay into a vessel, placed it in fire, and waited. The pottery fragment recovered from the Odai Yamamoto I site (大平山元I遺跡) in Aomori Prefecture has been radiocarbon-dated to approximately 16,500 years before present -- the oldest confirmed pottery in the world. It predates the earliest Mesopotamian ceramics by more than four millennia.

The conventional narrative of civilization links pottery to agriculture: grain needs storing, food needs cooking, therefore vessels follow farming. But the Jomon were not farmers. They were hunter-gatherers who invented pottery before any known society on the planet had planted a crop. This single fact dismantles the Western-derived model of civilizational progress -- the assumption that the sequence must run agriculture, then settlement, then technology (see Chapter 5, 'The Western Bias of the Four Great Civilizations').

The most persuasive explanation is what might be called the 'boiling revolution.' Tree nuts abundant in the Jomon forests -- acorns, horse chestnuts, buckeyes -- are inedible raw due to high tannin content. Removing those toxins requires prolonged boiling, and prolonged boiling requires a vessel that can withstand sustained heat. The Jomon did not invent pottery to store surplus. They invented it to unlock food that was otherwise poisonous. Pottery was not a consequence of abundance; it was a technology of survival in the forest.

What confounds explanation, however, is the sheer extravagance of Jomon pottery. If function were the sole driver, the vessels could have remained plain. Instead, the Jomon produced the flame-style pottery (kaen-doki, 火焔型土器) -- soaring, coiling forms of almost hallucinatory complexity. When the artist Okamoto Taro (岡本太郎) encountered Jomon pottery at the Tokyo National Museum in 1951, he described the experience as 'a dialogue with the fourth dimension.' Pouring excessive beauty into utilitarian objects -- this impulse runs unbroken through sixteen millennia of Japanese craft, from Jomon ceramics to Edo lacquerware to contemporary industrial design (see Chapter 4, 'Fermentation Culture').

The strongest counterargument cites pottery fragments from Xianren Cave (仙人洞遺跡) in Jiangxi Province, China, claimed to be as old as 20,000 years. But those dates derive from surrounding sediment rather than from the pottery itself, and the methodology remains contested. The Odai Yamamoto I dating was performed directly on carbonized material adhering to the pottery surface, making it considerably more robust. Regardless of which site ultimately claims priority, the fundamental fact stands: one of the world's oldest ceramic traditions arose not in the cradle of agriculture but at the forested edge of a volcanic archipelago, among people who had no need for farming -- and who would continue to have no need for it for another ten thousand years.

From 266 CE to 413 CE. One hundred and fifty years of silence in the history of the Japanese archipelago.

The Chinese chronicle Wei Zhi (the 'Account of the Wa') records in meticulous detail the 3rd-century realm of Wa -- the rule of Queen Himiko of Yamatai. But after the final tributary entry in 266 CE, all record of Wa falls abruptly silent. When Wa next appears in Chinese histories, in 413 CE, it has become an almost unrecognizable nation.

Before the void, Wa was a society of fragmented small kingdoms governed by a queen wielding shamanistic authority. After the void, the Yamato polity was constructing colossal keyhole-shaped burial mounds, wielding iron weapons and horses, and unifying the archipelago from its power base in the Kinki region as a formidable military state. What happened?

The archaeological record only deepens the enigma. With the onset of the Kofun period (late 3rd century), objects appeared across the archipelago with startling suddenness: the distinctive keyhole-shaped tomb, vast arsenals of iron weaponry, horses and equestrian gear, gilt-bronze ornaments. None of these had any significant presence during the Yayoi period. Whether they evolved gradually from indigenous culture or were introduced all at once from outside remains a subject of fierce scholarly debate.

In 1948, the University of Tokyo's Egami Namio advanced the 'Horse-Rider Conquest Theory' -- the hypothesis that continental horse-riding peoples conquered the archipelago via the Korean Peninsula and established the Yamato dynasty. Though the mainstream of academia regards this theory skeptically, it persists as a compelling framework for explaining the abrupt transformations of the Kofun period.

And what DNA reveals is precisely this: dramatic genetic change during that very interval. As the 2021 Triple Structure Model demonstrated, a third ancestral population arrived during the Kofun period and decisively shaped the modern Japanese genome. During those 150 silent years, the gene pool of the archipelago was rewritten at its foundation. In the century and a half when written records fell mute, DNA speaks eloquently of something that occurred. Until the Imperial Household Agency permits excavation of the imperial tombs, the full truth remains shrouded in darkness.

September, 1872 — Meiji 5. Someone wrapped an iron knife in washi paper and wrote, in ink, 'Nintoku Emperor's Tomb' (仁徳帝陵). The knife had come from just beyond the moat's edge, not the mound itself. The antiquarian who wrote the note was Kashiwagi Kaichirō (柏木貨一郎). For the next 150 years, the wrapping paper and the artifact passed through the hands of the Meiji industrialist Masuda Takashi (益田孝) and vanished into private collection, out of scholarly view.

What these 'grave goods that escaped' put on trial is the very limit of Imperial Household mausolea discussed earlier in this chapter (→ Ch. 1 'The Door That Will Not Open — Imperial Mausolea and Forbidden DNA Research'). Daisen-ryō Kofun (大仙陵古墳) — attributed by tradition to Emperor Nintoku — is among the largest keyhole-shaped tumuli on Earth, yet no full-scale academic excavation of its interior has ever been permitted. The single most important monument of the Kofun period, the era in which the modern Japanese genome was finalized, has remained a black box into the Reiwa age.

Then in 2024, Kokugakuin University Museum (國學院大學博物館) acquired the long-lost collection. In June 2025 the university published the results of a joint study with Sakai City (堺市) and Nippon Steel Technology: the gilt-bronze-mounted knife, the armor fragments, and the Meiji-5 wrapping paper all prove consistent — by materials analysis — with fifth-century Daisen-ryō grave goods. The knife's construction is especially singular: thin gold-plated copper sheets joined with silver rivets, a combination unrecorded in any other fifth-century kofun artifact. In the workshops of the Yamato court, metalworking techniques were practiced whose shape cannot be reconstructed from the 5th-century finds alone.

But a boundary must be observed. That these items are 'grave goods of fifth-century Daisen-ryō Kofun' is confirmed by materials analysis and the 1872 documentation. That they 'belonged to Emperor Nintoku himself' remains hypothesis. The Imperial Household Agency's designation of the mausoleum is unchanged; no academic evidence attributes an occupant. What 2025 crossed was the question 'Are these Daisen-ryō artifacts?' The question 'Whose artifacts are they?' remains wide open.

And yet the announcement revealed a quiet paradox. Without opening the tomb, by gathering the fragments that escaped its moat 150 years ago, scholarship can approach the center of Kofun-period power. The real field of inquiry was not inside the black box but among the pieces scattered along its edge. Just as DNA has begun to speak for the silent interval in early Japan's history (→ Ch. 1 'The 150-Year Void — Lost Records and a Fault Line in DNA'), the Daisen announcement shows that paths around forbidden excavation exist — provided, of course, that someone thought to wrap an artifact in paper and keep it safe for a century and a half.