 How long did it take for Venus’s conditions to mutate its human colonies? What is the purpose of these mutations?
DOUBLECROSS by JAMES Mac CREIGH Revolt was brewing on Venus, led by the descendant of the first Earthmen to land. [Transcriber's Note: This etext was produced from Planet Stories Winter 1944. "Everything shipshape, I take it!" But after all, they're human beings, just like us—" "Not any more. Four or five generations ago they were. "They had to acclimate themselves to Venus's climate. He stared at the wooden shacks that were the outskirts of the native city, dimly visible through the ever-present Venusian mist. The native guard of honor, posted a hundred yards from the Earth-ship, stood stolidly at attention with their old-fashioned proton-rifles slung over their backs. A few natives were gazing wonderingly at the great ship, but made no move to pass the line of guards. They think there will be hordes of immigrants from Earth, now that we know Venus is habitable. And there's some sort of a paltry underground group that is spreading the word that the immigrants will drive the native Venusians—the descendants of the first expedition, that is—right down into the mud. After all, the fittest survive. "From their own mouths you have heard it. Our parents came from Earth. "Then we must act. We have agreed that, if the Earth-ship returns, it means disaster for Venus. Therefore, it must not return."
 Four or five generations. Acclimation.
 Three or four generations. Hunting.  Four or five generations. Acclimation.  Four or five generations. Bomb making.  One or two generations. Revolution.