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Researchers have sequenced the genomes of Bronze Age humans and found evidence of hepatitis B virus (HBV) in 25 of 304 individuals across a span of 4000 years, suggesting that humans throughout Eurasia have been infected with HBV for thousands of years. In the first study, published in Nature, the international investigator team analysed ancient DNA sequences from 304 central and western Eurasian humans, who lived between about 2000 and 7000 years ago. They found evidence of HBV infections in 25 individuals who had lived between 800 and 4500 years ago. The authors recovered 12 full or partial HBV genomes — including genotypes that are now extinct — that they compared with modern human and non-human primate HBV genomes. They found that ancient HBV genomes existed in regions incongruent with the present day distribution of the virus, and identified at least one now extinct genotype. Discovery of further ancient viral sequences may provide a clearer picture of the true origin and early history of HBV, and advance understanding of the contributions of natural and cultural changes to disease burden and mortality. In a related study, also published in Nature, the multinational research team sequenced the genomes of 137 ancient humans from the Eurasian steppes — a vast region spanning about 8000 km from Hungary to northeastern China — from the period 2500 bc to ad 1500. They also genotyped 502 present day individuals with self-reported ancestries from across Central Asia, the Altai, Siberia and the Caucasus. Their findings shed light on the population history of the region, suggesting a gradual transition from Bronze Age Indo-European pastoralists of West Eurasian origin toward a society of mounted warriors of primarily East Asian ancestry.