"The Enchanted Forest", a novelette by Fritz Leiber, first published in Astounding Science Fiction, October 1950, available at the Internet Archive. Does any of these covers look familiar?
The director nodded. "On Magellanic 47 we're carrying on that same sort of work, not with rats, but with human beings. The cages are half-mile clearings with identical weather, terrain, plants, animals—everything identical down to the tiniest detail. The bars of the cages are the thorn trees, which our botanists developed specially for the purpose. The inmates of the cages—the human experimental animals—are identical twins—though centuplets would be closer to the right word. Identical upbringings are assured for each group by the use of robot nurses and mentors, set to perform always the same unvarying routine. These robots are removed when the members of the group are sufficiently mature for our purposes. All our observations are, of course, completely secret—and also intermittent, which had the unfortunate result of letting Elven do some serious damage before he was caught.
"Do you see the setup now? In the thorn forest in which Elven was wrecked there were approximately one hundred identical clearings set at identical intervals. Each clearing looked exactly like the other, and each contained one Sefora, one Tulya, one Alfors, and one Kors. Elven thought he was going in a circle, but actually he was going in a straight line. Each evening it was a different clearing he came to. Each night he met a new Sefora.
"Each group he encountered was identical except for one factor—the factor we were varying—and that had the effect of making it a bit more grisly for him. You see, in those groups we happened to be running an experiment to determine the causes of human behavior patterns toward strangers. We'd made slight variations in their environment and robot-education, with the result that the first group he met was submissive toward strangers; the second was violently hostile; the third as violently friendly; the fourth highly
suspicious. Too bad he didn't meet the fourth group first—though, of course, they'd have been unable to manage him except that he was half mad with supernatural terror."
