There seems to be at least one common denominator to all intelligent life: it was bipedal and bimannual. Four legs was the most practical number for any animal on any planet, and it seems that nature has nothing else to work with. When she decided to give intelligence to a species, she taught him to stand on his hind legs, freeing his forefeet to become tools of his intellect. And she usually taught him by making him use his hands to climb. As a Cophian biologist had said, "Life first tries to climb a tree to get to the stars. When it fails, it comes down and invents the high-C drive.

Author: Walter M. Miller Jr.