Greg Mayer, as part of a charming larger piece, relates a back and forth he had with some students a few days ago on whether or to what extent we and alien intelligent life forms would be able to identify each other as intelligent life forms:
I mentioned to the students that I’d seen a great web post that morning about first contact with aliens (h/t: PZ), which stressed the likely lack of similarity and extreme technological disparity between us and interstellar travelers (“nuclear weapons [used by them] vs. sponges [which would be us]“), and how a binary code would be the way to communicate, although PZ noted they’d probably collect several specimens for the interstellar natural history museum before they figured out the sponges [that would be us] were sentient. The grad student suggested that it wouldn’t be that bad, since convergent evolution would insure that they had some basic similarities to us. I said I’m not so sure, and noted that George Gaylord Simpson, in his famous essay on the nonprevalence of humanoids (link might require subscription), had argued strongly that life elsewhere is decidedly unlikely to be familiar to us. We discussed what basic similarities there might be among life forms evolved completely independently. Bilateral symmetry? Common on earth, but how many times had it evolved independently here? Cephalization? There were some interesting cases of it evolving in primitively radial urchins. Carbon based? It beats silicon, but there was the Horta on Star Trek.
We went on to note that there were ways of trying to distinguish independent from convergent origins. Shared, yet arbitrary, characteristics, such as the genetic code, suggest a single origin (unless of course there are functional differences among possible codes, which would make them non-arbitrary), while clearly adaptive similarities might arise through convergence (see whales and icthyosaurs).