By 3.2 billion years ago, Duplodnaviria viruses perfected the HK97-type capsid, a structural “shipping container” that protects DNA under immense pressure. This ancient blueprint proved so effective that it remains the shared machinery for both modern bacterial phages and human herpesviruses, bridging the gap between simple and complex life.

By 2.75 billion years ago, emerging somewhat nearer to the era of LUCA, Varidnaviria specialized in the Double Jelly-Roll (DJR) capsid structure. This versatile “folding” technique allowed them to construct shells ranging from simple icosahedrons to the massive envelopes of Giant Viruses. They are the primary architects of the viral world, infecting everything from bacteria to humans.

By 1.25 billion years ago, complex eukaryotes diversified, Retroviruses evolved by equipping mobile genetic elements (retrotransposons) with “stolen” structural proteins. Using the enzyme reverse transcriptase, they flip the flow of information from RNA back into DNA, allowing them to stitch themselves permanently into the host’s genome and hide for generations.