There was once two unfriendly microbiologists, who wished to maximize their exclusive genetic fitness.

The first biologist collected all the worst pandemics of mankind, combined them, reduced their lethality and added the module to inseminate infected females with a copy of his genome. The virus spread rapidly, and hundreds of his children were born, but with time vaccines were developed for the pandemics and, through their similarity, the virus was soon defeated.

The other biologist took samples of skin and blood, sequenced genomes, and found out which traces of foreign DNA were truly the most common amongst all humans. Finally he chose one virus, barely known, nigh impossible to track down or study, and modified it to inject his DNA in parallel with that of the infected, rigged up include the copy of hers as well as the virus during meiosis. Generations later, humanity created an AI to tile the universe with the genome they all shared.

(EDIT: I do not necessarily endorse the obvius moral of the story, it's MOSTLY a story, with rising discussion as a nice possible bonus.)