The Krithians arrived on Earth a while back. They discovered a planet (obviously) devoid of intelligent life. But being the curious Krithians that they are, they set about trying to solve the mystery of how so many useful tools ended up on a planet with no intelligent life.

Their initial guesses included such theories as might conclude that intelligent life outside of Earth itself actually created the machinery, brought it to earth, and then left it behind when they left.

This was quickly disregarded as sensible because, they concluded, if there was an intelligent design to this machinery, then surely the designer would have created a different design and mechanism for each of the functions of the tools. Instead, whether the tool functioned on land or on sea or in the air, though the machines may have differed in appearance, they all shared the same basic technology and materials.

Realizing this, they began to develop a new theory: All of the machinery evolved from simple inanimate objects. That is why they are basically the same technologies – either internal combustion, electric, or nuclear (the Krithians pronounce it "NOO-kyoo-lur") – they're all basically the same concept. (Krithians have already developed beyond mechanical travel and can tele-transport for at least small distances).

And, as if the similarity in technologies weren't sufficient observable data upon which to conclude the evolution devoid of intelligent design, they also observed the evolution of species. It was so apparent, if not visually, then by the fact that they actually have names above their bumpers, that the automobile (they call them "the wheel-thingys". Though Krithians are highly developed in matters of transport, they are somewhat lacking in erudite nomeclature)

…anyway, they noticed that the automobiles had OBVIOUSLY evolved. They noted that some, like the Mustang and the Thunderbird had evolved steadily, though showed signs of throw-back genes that would still, from time to time, manifest themselves. They noticed that some automobiles went extinct as they were too ugly too survive. The Edsel, the AMC Pacer and Gremlin (and they couldn't help but note that the mutant throwback, the PT Crusier, appearing at least 75% genetically identical to the AMC Pacer, was probably doomed to the same fate) were all ill-equiped for the environmental change that taste was going to foist upon them unawares.