Genesis: A Science Fiction/Short Story Claasic By H. Beam Piper!

Was this ill-fated expedition the end of a proud, old race--or the beginning of a new one? There are strange gaps in our records of the past. We find traces of man-like things--but, suddenly, man appears, far too much developed to be the "next step" in a well-linked chain of evolutionary evidence. Perhaps something like the events of this story furnishes the answer to the riddle.