Which story?--you mean "Life-line" or "Misfits", maybe?--I don't know what else Heinlein wrote in 1939. I don't remember noticing that as a major theme in Heinlein's work until after Sturgeon started emphasizing it c. 1953 (though there's hints of it in his earlier writing), but of course I haven't read all of Heinlein's stuff. I'd also assume both he and Sturgeon were influenced in that by earlier pulp writers whose names might not have survived for posterity--just about every later SF theme was experimented with in the pulps in the 1930s.