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.

For fifty years he had tried to colonize Mars and all his efforts had failed. Besides this dome which had been built for us there was only one other outpost, another glassite dome much smaller and less than a mile away.

It had looked as though mankind could never spread to the other planets of the solar system besides Earth for of all of them Mars was the least inhospitable; if he couldn't live here there was no use even trying to colonize the others.

And then, in 2034, thirty years ago, a brilliant biochemist named Waymoth had discovered daptine. A miracle drug that worked not on the animal or person to whom it was given, but on the progeny he conceived during a limited period of time after inoculation.

It gave his progeny almost limitless adaptability to changing conditions, provided the changes were made gradually.

Dr. Waymoth had inoculated and then mated a pair of guinea pigs; they had borne a litter of five and by placing each member of the litter under different and gradually changing conditions, he had obtained amazing results. When they attained maturity one of those guinea pigs was living comfortably at a temperature of forty below zero Fahrenheit, another was quite happy at a hundred and fifty above. A third was thriving on a diet that would have been deadly poison for an ordinary animal and a fourth was contented under a constant X-ray bombardment that would have killed one of its parents within minutes.

Subsequent experiments with many litters showed that animals who had been adapted to similar conditions bred true and their progeny was conditioned from birth to live under those conditions.

"Ten years later, ten years ago," the Head Teacher told us, "you children were born. Born of parents carefully selected from those who volunteered for the experiment. And from birth you have been brought up under carefully controlled and gradually changing conditions.

"From the time you were born the air you have breathed has been very 

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