This week, rereading the chapter in Jared Diamond's GUNS, GERMS, AND STEEL about domesticable animals reminded me of a short story I read a long time ago. The crew of a Terran spaceship gets marooned on a planet with a mild climate and no sapient inhabitants. One day they happen to be frolicking naked in a warm rain shower when an alien ship drops by and captures them as zoological specimens, mistaking them for native animals of the planet. The crew members are confined in a zoo on the aliens' world. They strive to find a way to demonstrate their intelligence to their captors. The aliens don't recognize their verbal sounds as language. The captives' attempts to write mathematical formulas, solar system diagrams, etc. in the dirt are ignored. When they build miniature structures out of sticks and stones, the aliens think they're nesting—and respond by moving the women into the men's cage so the "specimens" can breed! Meanwhile, the bored Earth people start taming a small, rodent-like animal that infests the enclosure. Eventually they construct a makeshift cage for their pet. As soon as the aliens notice this artifact, they release the captives and start serious attempts to communicate. Explanation: "Only intelligent beings put other beings in cages."
Unfortunately, this sardonic moral isn't entirely accurate. Some species of ants, for instance, keep aphids as "livestock" (although I don't suppose they build cages for them). So there's no guarantee this trick would work for the next group of Terrans locked in an extraterrestrial zoo. Recent research has shown, in fact, that some animals perform many of the acts previously thought unique to the human species (including, regrettably, rape and warfare). If you found yourself in a plight similar to that of the characters in this story, how would you prove to technologically superior aliens that you're a sapient being?
A related disturbing thought: Suppose dolphins have a level of intellect and social complexity equal to our own, and the only reason we haven't recognized this fact is that they don't produce the material technology we tend to consider an essential component of "human" intelligence?