Aliens: They know about handshakes, and everything!
In October 1957, the Russian satellite Sputnik became the first man-made object ever to be sent beyond earth's atmosphere. The launch -- the first time we knew for sure that we could propel pieces of ourselves out into space -- brought a new flurry of questions, one of them being the old standby: Is there life beyond us out there in the universe?
In November 1957, This Week Magazine offered a (semi-)scientific analysis of that question. Its conclusion: yeah, probably. Its further conclusion: Whatever life might be out there ... probably looks a lot like us humans. In a summary of that article, in February 1958, Science Digest declared that "we can be almost certain that our visitors from space will not have three eyes, webbed feet, or television antennae growing out of their foreheads." Because "instead, scientists theorize, they will probably bear a strong resemblance to the man next door."
Among other things, scientists theorize, "the man from Planet X" most likely: breathes air; eats both plants and meat; is approximately the same size as a human, weighing "at least 40 pounds, and probably more"; has a skull or a skull-like structure; has two eyes and two ears, both of them located near the brain; walks upright; and has -- scare quotes theirs -- "hands" and "feet." (Why not tentacles, sea creature-style? "Because tentacles can pull, but cannot push effectively.")
So. Instead of the acid-spewing aliens of Prometheus or the tentacletastic creatures of Independence Day, the extraterrestrials of 1958 were humanoid enough to share our basic biology -- and, judging from the illustration above, to have developed the handshake as their default gesture of greeting. What a lucky coincidence! How lovely to think of a universe populated not by mysterious Others, but by white-collared, courteous cosmomates! How nice to assume that "the kind of creature that could pay us a visit would have to be essentially like ourselves."