[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 gotshortened to daptine. It let us adapt. They explained it all to us when we were ten years old; I guess theythought we were too young to understand before then, although we knew alot of it already. They told us just after we landed on Mars. "You're _home_, children, " the Head Teacher told us after we had goneinto the glassite dome they'd built for us there. And he told us there'dbe a special lecture for us that evening, an important one that wemust 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, ofcourse, because the temperature in the dome was comfortable for us butalready freezing cold for him and the air was already too thin for himto breathe. His voice came to us by radio from inside his helmet. "Children, " he said, "you are home. This is Mars, the planet on whichyou will spend the rest of your lives. You are Martians, the firstMartians. 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 spendincreasingly long periods outdoors. "Then you will go forth and make your own homes, live your own lives, asMartians. You will intermarry and your children will breed true. Theytoo will be Martians. "It is time you were told the history of this great experiment of whicheach of you is a part. " Then he told us. Man, he said, had first reached Mars in 1985. It had been uninhabited byintelligent life (there is plenty of plant life and a few varieties ofnon-flying insects) and he had found it by terrestrial standardsuninhabitable. Man could survive on Mars only by living inside glassitedomes and wearing space suits when he went outside of them. Except byday in the warmer seasons it was too cold for him. The air was too thinfor him to breathe and long exposure to sunlight--less filtered of raysharmful to him than on Earth because of the lesser atmosphere--couldkill him. The plants were chemically alien to him and he could not eatthem; he had to bring all his food from Earth or grow it in hydroponictanks. * * * * * For fifty years he had tried to colonize Mars and all his efforts hadfailed. Besides this dome which had been built for us there was only oneother outpost, another glassite dome much smaller and less than a mileaway. It had looked as though mankind could never spread to the other planetsof the solar system besides Earth for of all of them Mars was the leastinhospitable; if he couldn't live here there was no use even trying tocolonize the others. And then, in 2034, thirty years ago, a brilliant biochemist namedWaymoth had discovered daptine. A miracle drug that worked not on theanimal or person to whom it was given, but on the progeny he conceivedduring a limited period of time after inoculation. It gave his progeny almost limitless adaptability to changingconditions, provided the changes were made gradually. Dr. Waymoth had inoculated and then mated a pair of guinea pigs; theyhad borne a litter of five and by placing each member of the litterunder different and gradually changing conditions, he had obtainedamazing results. When they attained maturity one of those guinea pigswas living comfortably at a temperature of forty below zero Fahrenheit, another was quite happy at a hundred and fifty above. A third wasthriving on a diet that would have been deadly poison for an ordinaryanimal and a fourth was contented under a constant X-ray bombardmentthat would have killed one of its parents within minutes. Subsequent experiments with many litters showed that animals who hadbeen adapted to similar conditions bred true and their progeny wasconditioned from birth to live under those conditions. "Ten years later, ten years ago, " the Head Teacher told us, "youchildren were born. Born of parents carefully selected from those whovolunteered for the experiment. And from birth you have been brought upunder carefully controlled and gradually changing conditions. "From the time you were born the air you have breathed has been verygradually thinned and its oxygen content reduced. Your lungs havecompensated by becoming much greater in capacity, which is why yourchests are so much larger than those of your teachers and attendants;when you are fully mature and are breathing air like that of Mars, thedifference will be even greater. "Your bodies are growing fur to enable you to stand the increasing cold. You are comfortable now under conditions which would kill ordinarypeople quickly. Since you were four years old your nurses and teachershave had to wear special protection to survive conditions that seemnormal to you. "In another ten years, at maturity, you will be completely acclimated toMars. Its air will be your air; its food plants your food. Its extremesof temperature will be easy for you to endure and its mediantemperatures pleasant to you. Already, because of the five years wespent in space under gradually decreased gravitational pull, the gravityof Mars seems normal to you. "It will be your planet, to live on and to populate. You are thechildren of Earth but you are the first Martians. " Of course we had known a lot of those things already. * * * * * The last year was the best. By then the air inside the dome--except forthe pressurized parts where our teachers and attendants live--was almostlike that outside, and we were allowed out for increasingly longperiods. It is good to be in the open. The last few months they relaxed segregation of the sexes so we couldbegin choosing mates, although they told us there is to be no marriageuntil after the final day, after our full clearance. Choosing was notdifficult in my case. I had made my choice long since and I'd felt surethat she felt the same way; I was right. Tomorrow is the day of our freedom. Tomorrow we will be Martians, _the_Martians. Tomorrow we shall take over the planet. Some among us are impatient, have been impatient for weeks now, butwiser counsel prevailed and we are waiting. We have waited twenty yearsand we can wait until the final day. And tomorrow is the final day. Tomorrow, at a signal, we will kill the teachers and the other Earthmenamong us before we go forth. They do not suspect, so it will be easy. We have dissimulated for years now, and they do not know how we hatethem. They do not know how disgusting and hideous we find them, withtheir ugly misshapen bodies, so narrow-shouldered and tiny-chested, their weak sibilant voices that need amplification to carry in ourMartian air, and above all their white pasty hairless skins. We shall kill them and then we shall go and smash the other dome so allthe Earthmen there will die too. If more Earthmen ever come to punish us, we can live and hide in thehills where they'll never find us. And if they try to build more domeshere we'll smash them. We want no more to do with Earth. This is our planet and we want no aliens. Keep off! Transcriber's Note: This etext was produced from _Amazing Stories_ March 1954. Extensive research did not uncover any evidence that the U. S. Copyright on this publication was renewed. Minor spelling and typographical errors have been corrected without note.