A joint study by French and Czech scientists involving the Optics and Biosciences Laboratory has just carried out the first analysis of the presence of specific DNA structures, known as G-quadruplexes, in ancient genomes of the hepatitis B virus, some of which date back as far as 10,000 years. This study reveals that the proportion of G-quadruplexes in these genomes has increased over the millennia, becoming close to that of the current human genome.