Philip K. Dick 
Beyond Lies the Wub 

“We are a very old race, ” the wub said. “Very old and very ponderous. It is difficult for us to move around. You can appreciate that anything so slow and heavy would be at the mercy of more agile forms of life. There was no use in our relying on physical defenses. How could we win? Too heavy to run, too soft to fight, too good-natured to hunt for game—”