Intelligent life evolved in the universe – 0nce. The First Intelligent Species became spacefaring but, unlike the adventures depicted in most science fiction, they found an uninhabited universe. Non-intelligent species were too rudimentary or too far away to be detected. Thus, as both a memorial to themselves and to enliven the universe, the First Intelligent Species seeded the necessary DNA for the eventual evolution of intelligent life in the primordial oceans of every planet that could support life. The First Intelligent Species did not only design the DNA to evolve intelligently, but to parallel their own evolution. An application of the idea that “ontogeny recapitulates phylogeny” on the scale of life itself. Our corner of the universe thereby became the home of Vulcans, Romulans, Cardassians, Humans, Betazoids, and other hominid species which are all decedents of the First Intelligent Species. Therefore, in the eyes of the universe, the many hominid species are closely related despite their disparate home planets.
Of course, the theory itself is science fiction, but the mental exercise helps the scientist to enjoy science fiction, no matter how cheesy the alien design. As a bonus, the graphic at the article has twenty aliens you are invited to help identify. Link