"Yes. And the apes turn into lower creatures. Those become lower creatures still." Sadau's eyes were earnest and doleful. "The process may run back and down to the worm, for all we can judge. We try not to think too much about it."
"This is a joke of some kind," protested Parr, but Sadau was not smiling.
"Martian joke, perhaps. The treaty keeps them from killing us—and this is their alternative punishment. It makes death trivial by comparison.... You don't believe. It's hard. But you see that some of us, oldest in point of exile, are sliding back into bestiality. And you saw us drive away, as our custom is, a man who had definitely become a beast."
"That thing was a man?" prompted Parr, his spine chilling.
"It had been a man. As you wander here and there, you'll come upon queer sights—sickening ones."
Parr squinted at the huts, around the doors of which lounged the other men. "That looks like a permanent community, Sadau."
"It is, but the population's floating. I came here three months ago—Earth months—and the place was operating under the rules I outlined. Latest comer, necessarily the highest-grade human being, to be chief; those who degenerate beyond a certain point to be driven out; the rest to live peaceably together, helping each other."
Parr only half heard him. "Evolution turned backward—it can't be true. It's against nature."
"Martians war against nature," replied Sadau pithily. "Mars is a dead world, and its people are devils. They'd be the logical explorers to find a place where such things can be, and to make use of it. Don't believe me if you don't want to. Time and life here will convince you."