 What is one way the story’s setting, Venus, affects the characters and and sets up the plot?
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. Extensive research did not uncover any evidence that the U.S. copyright on this publication was renewed.] The Officer of the Deck was pleased as he returned to the main lock. There was no reason why everything shouldn't have been functioning perfectly, of course, but he was pleased to have it confirmed, all the same. The Executive Officer was moodily smoking a cigarette in the open lock, staring out over the dank Venusian terrain at the native town. "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. That's a basic law of—" The annunciator over the open lock clanged vigorously, and a metallic voice rasped: "Officer of the Deck! Instruments reports a spy ray focused on the main lock!" But even while he was giving orders, the warning light flickered suddenly and went out. "From their own mouths you have heard it. Our parents came from Earth. "Then we must act. The Council has told us that we alone will decide our course of action. We have agreed that, if the Earth-ship returns, it means disaster for Venus. Therefore, it must not return." "No. But they will never get back to Earth." "The Council did not know what we would face. The Councilmen could not come to the city and see what strength the Earth-ship has." Like the girl, the old man retreated before his eyes.
 Over the last four or five generations, Venus’s conditions have caused its human colony to mutate in order to better survive. Differences in appearance cause a racial rift between humans from Earth and humans from Venus, which sets the story’s plot by imposing tension between the two groups.
 The story takes place on Mars, not Venus. Over the last four or five generations, Mars’ conditions have caused its human colony to mutate in order to better survive. This causes a racial rift between humans from Earth and humans from Mars, which sets the story’s plot by imposing tension between the two groups.  Over the last four or five generations, Venus’s conditions have caused its human colony to mutate in order to better survive. Differences in appearance cause a racial rift between humans from Earth and humans from Venus, which sets the story’s plot by imposing tension between the two groups.  Over the last fifteen generations, Venus’s conditions have caused its human colony to mutate in order to better survive. This causes a racial rift between humans from Earth and humans from Venus, which sets the story’s plot by showing Venusians in a bad light.  Over the last two or three generations, Venus’s conditions have caused its human colony to mutate into swamp people. This causes a holocaust of humans from Venus, which sets the story’s plot by imposing tension between the two groups.