Keith Laumer 
Cocoon 

Two Billion Years ago, a unit of life had the urge to climb out of the sea. It died. But that didn’t count. The urge to climb out was the thing—greater in its force than a million suns to keep the urge is the measure of man. Before becoming a science fiction writer Laumer was an officer in the United States Air Force and a diplomat in the Foreign Service, adding a note of realism to many of his stories. One of science fiction’s true luminaries