Produced by Greg Weeks, Stephen Blundell and the Online Distributed Proofreading Team at http://www.pgdp.net [Illustration] KEEP OUT BY FREDERIC BROWN _With no more room left on Earth, and with Mars hanging up there empty of life, somebody hit on the plan of starting a colony on the Red Planet. It meant changing the habits and physical structure of the immigrants, but that worked out fine. In fact, every possible factor was covered--except one of the flaws of human nature...._ Daptine is the secret of it. Adaptine, they called it first; then it got shortened to daptine. It let us adapt. They explained it all to us when we were ten years old; I guess they thought we were too young to understand before then, although we knew a lot of it already. They told us just after we landed on Mars. "You're _home_, children," the Head Teacher told us after we had gone into the glassite dome they'd built for us there. And he told us there'd be a special lecture for us that evening, an important one that we must all attend. And that evening he told us the whole story and the whys and wherefores. He stood up before us. He had to wear a heated space suit and helmet, of course, because the temperature in the dome was comfortable for us but already freezing cold for him and the air was already too thin for him to breathe. His voice came to us by radio from inside his helmet. "Children," he said, "you are home. This is Mars, the planet on which you will spend the rest of your lives. You are Martians, the first Martians. You have lived five years on Earth and another five in space. Now you will spend ten years, until you are adults, in this dome, although toward the end of that time you will be allowed to spend increasingly long periods outdoors. "Then you will go forth and make your own homes, live your own lives, as Martians. You will intermarry and your children will breed true. They too will be Martians. "It is time you were told the history of this great experiment of which each of you is a part." Then he told us. Man, he said, had first reached Mars in 1985. It had been uninhabited by intelligent life (there is plenty of plant life and a few varieties of non-flying insects) and he had found it by terrestrial standards uninhabitable. Man could survive on Mars only by living inside glassite domes and wearing space suits when he went outside of them. Except by day in the warmer seasons it was too cold for him. The air was too thin for him to breathe and long exposure to sunlight--less filtered of rays harmful to him than on Earth because of the lesser atmosphere--could kill him. The plants were chemically alien to him and he could not eat them; he had to bring all his food from Earth or grow it in hydroponic tanks. * * * * *